how to create a decorator proxy page in asp.net 3.5

I am trying to make this feature, and I'm really stuck.

I have two applications that run on the same domain. and I need to have one application load pages from the other one inside it's own (the first) master page.

I have full control of the code of both sides, of course.

I have tries using HTTPRequest, and HTTPResponse, and I have tried using WebBrowser. Both work great as long as I have static(plain HTML) pages. However, those pages are actually dynamic. the user need to press server-side buttons (postback) and generally use the session, viewstate, and/or cookies.

because of that, HTTPRequest and WebBrowser fail me, as they do not cause postback, and therefore those server-side controls are not working. more so, if I try to "fake" a postback by saving the ViewState after each response and than resend it on the next request, after a few (3-4) times the original page will return a "The state information is invalid for this page and might be corrupted" error, even if I use

EnableViewStateMac ="false" EnableSessionState="True" EnableEventValidation ="false" ValidateRequest ="false" ViewStateEncryptionMode ="Never

So... any ideas how can I solve this issue?

Thanks in advance