You intend do to controlled test shots?!?!? Blasphemy!
Actually, I taped my Holga a lot to get rid of the light leaks. I even eliminated most of them! Mine has huge vignetting, but that's about what I was hoping for. The bulb feature is great, btw! I do night shots a lot at the moment and am getting pretty good at guessing. It's fun, isn't it.