I was a little overwhelmed by the reaction to my custom GINA. The good thing about it is that it motivated me to put a better version out that addresses all the comments I had so far, namely :
Allow force log off without being a member of the administrator group
Allow an arbitrary group to be excluded from this GINA unlock policy
Show a notice that a custom GINA is in place
I also put up a permanent page for the project. It has better documentation and fancy graphics. Enjoy !