diff --git a/sdk/sdk_test.go b/sdk/sdk_test.go
index a13b0d7..97fb248 100644
--- a/sdk/sdk_test.go
+++ b/sdk/sdk_test.go
@@ -565,6 +565,49 @@
 		)
 	})
 
+	t.Run("SOONG_SDK_SNAPSHOT_USE_SOURCE_CONFIG_VAR=module:build_from_source", func(t *testing.T) {
+		result := android.GroupFixturePreparers(
+			preparer,
+			android.FixtureMergeEnv(map[string]string{
+				"SOONG_SDK_SNAPSHOT_USE_SOURCE_CONFIG_VAR": "module:build_from_source",
+			}),
+		).RunTest(t)
+
+		checkZipFile(t, result, "out/soong/.intermediates/mysdk/common_os/mysdk-current.zip")
+
+		CheckSnapshot(t, result, "mysdk", "",
+			checkAndroidBpContents(`
+// This is auto-generated. DO NOT EDIT.
+
+java_import {
+    name: "mysdk_myjavalib@current",
+    sdk_member_name: "myjavalib",
+    visibility: ["//visibility:public"],
+    apex_available: ["//apex_available:platform"],
+    jars: ["java/myjavalib.jar"],
+}
+
+java_import {
+    name: "myjavalib",
+    prefer: false,
+    use_source_config_var: {
+        config_namespace: "module",
+        var_name: "build_from_source",
+    },
+    visibility: ["//visibility:public"],
+    apex_available: ["//apex_available:platform"],
+    jars: ["java/myjavalib.jar"],
+}
+
+sdk_snapshot {
+    name: "mysdk@current",
+    visibility: ["//visibility:public"],
+    java_header_libs: ["mysdk_myjavalib@current"],
+}
+			`),
+		)
+	})
+
 	t.Run("SOONG_SDK_SNAPSHOT_VERSION=unversioned", func(t *testing.T) {
 		result := android.GroupFixturePreparers(
 			preparer,
diff --git a/sdk/update.go b/sdk/update.go
index b146b62..6da3756 100644
--- a/sdk/update.go
+++ b/sdk/update.go
@@ -35,6 +35,37 @@
 //     By default every unversioned module in the generated snapshot has prefer: false. Building it
 //     with SOONG_SDK_SNAPSHOT_PREFER=true will force them to use prefer: true.
 //
+// SOONG_SDK_SNAPSHOT_USE_SOURCE_CONFIG_VAR
+//     If set this specifies the Soong config var that can be used to control whether the prebuilt
+//     modules from the generated snapshot or the original source modules. Values must be a colon
+//     separated pair of strings, the first of which is the Soong config namespace, and the second
+//     is the name of the variable within that namespace.
+//
+//     The config namespace and var name are used to set the `use_source_config_var` property. That
+//     in turn will cause the generated prebuilts to use the soong config variable to select whether
+//     source or the prebuilt is used.
+//     e.g. If an sdk snapshot is built using:
+//       m SOONG_SDK_SNAPSHOT_USE_SOURCE_CONFIG_VAR=acme:build_from_source sdkextensions-sdk
+//     Then the resulting snapshot will include:
+//       use_source_config_var: {
+//         config_namespace: "acme",
+//         var_name: "build_from_source",
+//       }
+//
+//     Assuming that the config variable is defined in .mk using something like:
+//       $(call add_soong_config_namespace,acme)
+//       $(call add_soong_config_var_value,acme,build_from_source,true)
+//
+//     Then when the snapshot is unpacked in the repository it will have the following behavior:
+//       m droid - will use the sdkextensions-sdk prebuilts if present. Otherwise, it will use the
+//           sources.
+//       m SOONG_CONFIG_acme_build_from_source=true droid - will use the sdkextensions-sdk
+//            sources, if present. Otherwise, it will use the prebuilts.
+//
+//     This is a temporary mechanism to control the prefer flags and will be removed once a more
+//     maintainable solution has been implemented.
+//     TODO(b/174997203): Remove when no longer necessary.
+//
 // SOONG_SDK_SNAPSHOT_VERSION
 //     This provides control over the version of the generated snapshot.
 //
@@ -760,6 +791,8 @@
 	module.insertAfter("name", "sdk_member_name", name)
 	// Remove the prefer property if present as versioned modules never need marking with prefer.
 	module.removeProperty("prefer")
+	// Ditto for use_source_config_var
+	module.removeProperty("use_source_config_var")
 	return module
 }
 
@@ -1627,13 +1660,24 @@
 		// snapshot to be created that sets prefer: true.
 		// TODO(b/174997203): Remove once the ability to select the modules to prefer can be done
 		//  dynamically at build time not at snapshot generation time.
-		prefer := ctx.sdkMemberContext.Config().IsEnvTrue("SOONG_SDK_SNAPSHOT_PREFER")
+		config := ctx.sdkMemberContext.Config()
+		prefer := config.IsEnvTrue("SOONG_SDK_SNAPSHOT_PREFER")
 
 		// Set prefer. Setting this to false is not strictly required as that is the default but it does
 		// provide a convenient hook to post-process the generated Android.bp file, e.g. in tests to
 		// check the behavior when a prebuilt is preferred. It also makes it explicit what the default
 		// behavior is for the module.
 		bpModule.insertAfter("name", "prefer", prefer)
+
+		configVar := config.Getenv("SOONG_SDK_SNAPSHOT_USE_SOURCE_CONFIG_VAR")
+		if configVar != "" {
+			parts := strings.Split(configVar, ":")
+			cfp := android.ConfigVarProperties{
+				Config_namespace: proptools.StringPtr(parts[0]),
+				Var_name:         proptools.StringPtr(parts[1]),
+			}
+			bpModule.insertAfter("prefer", "use_source_config_var", cfp)
+		}
 	}
 
 	// Group the variants by os type.
diff --git a/ui/build/dumpvars.go b/ui/build/dumpvars.go
index 83c8865..f3c442e 100644
--- a/ui/build/dumpvars.go
+++ b/ui/build/dumpvars.go
@@ -163,6 +163,7 @@
 	"AUX_OS_VARIANT_LIST",
 	"PRODUCT_SOONG_NAMESPACES",
 	"SOONG_SDK_SNAPSHOT_PREFER",
+	"SOONG_SDK_SNAPSHOT_USE_SOURCE_CONFIG_VAR",
 	"SOONG_SDK_SNAPSHOT_VERSION",
 }