SVN Externals and Permissions in the absence of path based access control

Question

We are using SVN externals to basically create symbolic links to other repositories.
For example

svn://Repo1/Projects/Project1/Trunk

Contains some directories which are actually externals linking to

svn://Repo2/Projects/Derp_Library_Foo

When a user who only really needs access to Repo1 and the few externals linked in Repo2, we are forced to give full access to Repo2 otherwise they cannot checkout the path which contains externals to Repo2.
If we use path-based access control, we could easily create groups to manage this, but right now it is black or white: full access to the repo or none.

Is there any solution that doesn't involve using path-based access and doesn't involve duplicating the shared data/libraries?
We have SVN 1.6.11 using svnserve on Linux.

Answer 1

You have to grant RO access only to Repo2 in order to give user ability to checkout data from Repo1 with externals in Repo2