The linkbuttons I mentioned will be RSS links to other websites.
however, the design will be such that upon clicking these links, the user will be directed to a special popup, 'headlines'. There, the URL of the website with the news item will be entered server-side where it will be scraped for the relevant text in the feed. The text will then be displayed in the special headlines window.

Since the popup is being opened using javascript, and since the URL in question must remain secret, I wish to pass it as a session variable. (I believe ViewState would suffice as well)

You asked.