Updating cookie in client and aware server-side (ASP 3.0)

Question

Here's the scenario : I need to isolate session variables of my application when tabbed browsing on IE8.

I'd like to set an ID by tab using SessionStorage. How to access this ID from my ASP script code (server-side) ? Right now I'm using a cookie and reloading the page, but on cookie change and reload my server-code is executing twice...

I'm thinking about read cookie once in first page and then setting this ID in a hidden field, but this would mean I would have to :

1. Manually add this input to the forms in every pages (I cannot use an include file for that)
2. Take the prefix from the querystring

Can someone think in a different approach? Maybe smthing in jQuery to update cookie via webservices? Could it be possible?