I don’t know a lot about this issue in particular but I figure that unless your finger print reader is capable of hooking into the same framework that smartcards use you’re probably going to find it difficult if not impossible to accomplish. I’m also fairly sure that there’s no magic registry hack or logon script way to perform authentication. The only thing I can suggest in terms of investigating further is to look at how RSA, et al. hook into Windows authentication.
If you do investigate further I’m interested in hearing the results. If you don’t mind can you please send me a follow up if proceed?