Passing param tosame silverlight application in other window

Question

Hi all, i am having a silverlight application.
What i want to do is, On button click, open same application in other window by passing login credentials, and  use that credentials in other window for login process.
I tried with initparams, but every time i got its count as 0, i tried with fragmentation, it did work for me, but the problem was .xap file was downloaded everytime when I click on the button i.e for every new window .xap file was being downloaded.
How can I acheive it.
Thanks