Using WPMU with reverse proxies


I run a number of standalone wordpress blogs that have grown up over time on a number of hosts.

It's getting a real pain keeping them all patched and such and I found WPMU and it's looking like my saviour in terms of running them all off a single codebase.. awesome.

However so I don't lose all my search rankings I wrote myself a simple proxy script that I have put on the blogs original hosting that passes requests through to my WPMU server and then back to the browser, so it looks to the rest of the world as though nothing has changed and everything is on its own domain name and own hosting.. excellent again!

The one flaw is that anything that uses POST rather than GET doesn't work, so I can't login to my blogs and people can't post comments (well they can post them, but get only a blank screen after posting, no confirmation).

This is the last piece of the jigsaw for me and if I can get it fixed then it would all be perfect.

Can anyone help point me in a direction that could solve this last issue?