Well, a user is going to have to be logged in to retrieve any permissions to test on.  Once they are logged in, you can start swapping things around...I had posted a reply to you at some point about creating a custom login form...you can look at that to get an idea possibly.  But you will have to login in order to retrieve permissions (at least through the normal framework functionality).  You can use the SF security business objects and manually load the BO to get the data you want to look at before the login occurs.  That is really the only way I know how to answer you on this one .

I think this whole think has become much more complicated than it needs to be.  If it were me, I would adjust application to work within the confines of the security so I would not have to make a lot of changes.

For example, when a user comes into the application, they are going to have to choose which project to work on, right?  Why not do something with security at that point.  Or what if your projects allows certain users to associated with it, rather than trying to go the other way around. 

I don't know your application, but I do know that we can come up with a more simple solution that what you have been doing lately.  When it starts getting complicated like this...we always sit down as a team and figure out another avenue to travel.