>Shouldn't you be able to by using session variables? I know this does not stricly adheres to 'form authentication' and/or using web.config, but it is another aternative derived from 'old school' methods, no?

Well, yes of course you can create your own login scheme and deal with it manually, which is easy enough to do. If you have to you can even mount that into the regular Identity objects of ASP.NET to make it work like forms auth does.