diff --git a/cli/examples/custom-working-copy/main.rs b/cli/examples/custom-working-copy/main.rs
index 40bdcf4b4..b48e03157 100644
--- a/cli/examples/custom-working-copy/main.rs
+++ b/cli/examples/custom-working-copy/main.rs
@@ -34,7 +34,9 @@ use jj_lib::working_copy::{
     CheckoutError, CheckoutStats, LockedWorkingCopy, ResetError, SnapshotError, SnapshotOptions,
     WorkingCopy, WorkingCopyFactory, WorkingCopyStateError,
 };
-use jj_lib::workspace::{default_working_copy_factories, Workspace, WorkspaceInitError};
+use jj_lib::workspace::{
+    create_jj_dir, default_working_copy_factories, Workspace, WorkspaceInitError,
+};
 
 #[derive(clap::Parser, Clone, Debug)]
 enum CustomCommand {
@@ -58,6 +60,7 @@ fn run_custom_command(
             Workspace::init_with_factories(
                 command_helper.settings(),
                 wc_path,
+                create_jj_dir,
                 &backend_initializer,
                 Signer::from_settings(command_helper.settings())
                     .map_err(WorkspaceInitError::SignInit)?,
diff --git a/lib/src/workspace.rs b/lib/src/workspace.rs
index 49fe71477..067fa4aa1 100644
--- a/lib/src/workspace.rs
+++ b/lib/src/workspace.rs
@@ -87,7 +87,11 @@ pub struct Workspace {
     working_copy: Box<dyn WorkingCopy>,
 }
 
-fn create_jj_dir(workspace_root: &Path) -> Result<PathBuf, WorkspaceInitError> {
+/// Default function to create the .jj directory inside an existing repo
+/// directory.
+///
+/// Custom extensions can override this to do alternative initialization.
+pub fn create_jj_dir(workspace_root: &Path) -> Result<PathBuf, WorkspaceInitError> {
     let jj_dir = workspace_root.join(".jj");
     match std::fs::create_dir(&jj_dir).context(&jj_dir) {
         Ok(()) => Ok(jj_dir),
@@ -230,6 +234,7 @@ impl Workspace {
     pub fn init_with_factories(
         user_settings: &UserSettings,
         workspace_root: &Path,
+        jj_dir_creator: impl FnOnce(&Path) -> Result<PathBuf, WorkspaceInitError>,
         backend_initializer: &BackendInitializer,
         signer: Signer,
         op_store_initializer: &OpStoreInitializer,
@@ -239,7 +244,7 @@ impl Workspace {
         working_copy_factory: &dyn WorkingCopyFactory,
         workspace_id: WorkspaceId,
     ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
-        let jj_dir = create_jj_dir(workspace_root)?;
+        let jj_dir = jj_dir_creator(workspace_root)?;
         (|| {
             let repo_dir = jj_dir.join("repo");
             std::fs::create_dir(&repo_dir).context(&repo_dir)?;
@@ -284,6 +289,7 @@ impl Workspace {
         Self::init_with_factories(
             user_settings,
             workspace_root,
+            create_jj_dir,
             backend_initializer,
             signer,
             ReadonlyRepo::default_op_store_initializer(),