Destroying A Session And Starting It Back Up On The Same Page

I have a quick signup for a friends page, and at the end of the signup I wanna destroy all the session variables using the nice session.abandon then create two session variables for the username and password so they're already signed in, then redirect them to the index page already logged in. Problem is the session variables don't get saved on the redirect when the session has been abandoned on the page. If I take the abandon out and destroy the session variables individually everything works fine and the new session variables survive. But if I abandon the session then set the new variables they do not. Yes, they are being set after the abandon, and do exist as I've written them to the browser before the redirect. Its not that big a deal in such a small scale to delete all the variables individually, but theres gotta be a way incase it was hundreds of session variables right.