How To Port A ScriptManager UpdatePanel To A JQuery-based Solution

We are currently migrating the client part of a legacy webapp from asp.net ajax to jquery/jquery-ui. The app consists (among other things) of some asp.net ajax UpdatePanels.

Now I want to throw out all that __doPostback() stuff and talk with jQuery's $.ajax to the "server-side" of the .ascx controls. Ideally, the server reponds with some parseable Datastructure that I can throw into my jQuery UI controls.

I already realized that this is difficult to do, because the asp.net ajax client/server code is heavily interwoven and there are no public interfaces to hook into ajax requests or responses. However, we don't want to change the server-side code, because it should still run with the old asp.net frontend.

After some tweaking I found out that I can hook into ScriptManager's beforeRequest and endRequest events to get notified of postbacks and partial responses. I dispatch these to jQuery Events:

var paqeRequestInst = window.Sys.WebForms.PageRequestManager.getInstance();
//bind ASP.NET ScriptManager events to jQuery events
paqeRequestInst._events.addHandler('beforeRequest', function(){
$(window).trigger('beforePanelResponse');
});
paqeRequestInst._events.addHandler('endRequest', function(pageRequestInst, ErrInst){
$(window).trigger('afterPanelResponse', [pageRequestInst, ErrInst]);
});

However, a lot of questions remain:

What is the best way to intercept the ScriptManager Response, parse it, and throw it into my jQuery UI controls? How do I update all that __VIEWSTATE stuff, that is normally managed by the ScriptManager?
Are there best-practices/jquery-plugins for such a "asp.net ajax to jquery" scenario?