Have ye considered the Catalyst framework for all of this? There's a somewhat out-of-date Catalyst tutorial that does an app with both HTML and XMLRPC interfaces. Swap in one of the Catalyst::View::REST-style interfaces for XMLRPC, and with some digging, it might be adaptable to your needs. I know you can get the header information in Catalyst fairly easily, and call Private functions within it for your seamless front-end.
Edit: Looks like the Catalyst Cookbook covers XMLRPC, as well, taking ideas and examples from the above link.
Does that sound useful for you?
----Asim, known to some as Woodrow.