That is one of the challenges with Sharepoint is granular security. I do not think there is a way without using multiple libraries but then its a pain for those who can see all.
I typically secure my forms in SQL where you can have very granular permisisons, down to the document level. There is also a SharePoint web part for documents secured by SQL which will only show those forms which they have permission.
Send me an email if you would like to see an example.