I'm not quite convinced this should be part of the Visual Studio integration. I think it makes more sense to have a separate tool that captures the log messages on a given target (subversion file path or URL), and parses the log messages from there.
I would use SharpSvn to create a tool like that

svnsync is a process that's started from time to time to sync from one read/write repository to one or more read-only repositories. If you need read-only access you can use the intranet read-only repository, if you need write access you need to use the internet one.

In other words, this is not something that can or should be implemented by AnkhSVN.

Also see: http://subversion.tigris.org/svn_1.5_releasenotes.html#webdav-proxy
about write-through proxies. This allows you to commit to the read-only repository (which will forward your request to the internet one), and then svnsync changes back