Restricting HTTP access to a repository portion

I'd like to setup public access via HTTP/HTTPS to certain
subdirectories of my repository. In my tests with Apache2 and the
the SVNPath statement, it appears that SVNPath must point to the root
of the repository. That's reasonable. It'd be nice to have some
directive like SVNLocation that could set the location in the
repository that would be served.

For example, URL http://server/project1 accessing the directory
trunk/projects/p1 in repository /opt/svn/repos could use a syntax like:
  <Location /project1>
    SVNPath /opt/svn/repos
    SVNLocation trunk/projects/p1
  </Location>

As opposed to adding a new directive, is there any existing method I
could use for such functionality?

Thanks!

-- 
Kevin Rosenberg
kevin@rosenberg.net