Multiple Authentication styles for dav svn

Hello.

Apologies if this has been covered before, but I can't find mention of it
anywhere.

I have need for a multiple authentication system with SVN (+Apache),
switched on requesting IP.

Basically, I need:
a) internal users (matching a hostmask) authenticating via one passwd file
(with AuthzSVNAccessFile)
b) external users (not matching above hostmask) authenticating via a
different passwd file (with same AuthzSVNAccessFile)

I've got this working with multiple Location directives to the same
repository, but I'd like to have it handled transparently.

Also, I require groups and path-based authentication, so svnserve isn't
really an option.

Is this possible? Any thoughts?

Thanks.

--
Andy.