Accessing Report Services Using Form Authentication Against Active Directory

I hope someone can help.

I'm working on a web project that will display the reports in an iframe to the user. When I was using windows security It worked perfectly.

Now my boss wants me to use form based authentication instead that can authenticate against our current Active Directory. This is working perfectly and does authenticate correctly. The only problem is that when I load a report in the iframe http://myserver/reportserver/myreport-blah reporting services prompts the user to enter in windows credentials. Is there anyway to pass my form credentials to the report server so that the user doesn't have to log in again.

Both the report server and the web app are on the same server BUT in different virtual directories.

PS: I tried using the reportviewer control but it does not display things correctly. For example, I have use a multi select dropdown on the reports and it messes up the drop down when the user only has 1 selection (hiding the selection). If the user has more than one selection the drop down uses scroll bars. I would use the reportviewer control if it displayed exactly like it does when using alternate URL method.

Any help would be MUCH appreciated!

Thanks!