I find this post confusing. I understand REST to be centered around clean URLs. In that case, maybe CGI::Application::Dispatch is what you are looking for. It works well for me. You mentioned delivering XML, but that's not technically part of REST.

On the other hand, WWW::Mechanize should have little trouble retrieving XML. Your application just needs to serve it.

It would be helpful to see some more concrete examples or description of the problem you are running into.