This might be really hacky, but I'm beginning to get desperate
Is it possible to prevent a request from actually hitting the actual page...ie, can I write something in Application_BeginRequest that processes the part that I want, and then skips the rest of the lifecycle?
Oh, and is it possible to do it in such a way that the ajax update panel does throw a fit (return some default content that says, "I haven't done anything sorry")
Ok, mad question over.
Consider writing an HTTPModule sitting on the front of the request processing flow to take care of that.