There was a script posted here a while back that did that, but I'm afraid it was maya. Chameleon? edit: http://boards.polycount.net/showthread.php?p=828426 http://decalcreator.inlandstudios.com/
I like you're crazy thinkin, you might be able to use the align highlight or align camera and then snap a light to the camera... But I think that will get messy. I also like Eric's idea of using conform to wrap a piece of geo around another. But what I normally end up doing, is just copy some geo, push it so it floats…
You could beg some of the resident scripters to make something up for you perhaps? I know we had a couple brilliant mel scripters at the last place I worked cook up something like that. It gave you a plane contrained to your camera, which you could aim where you wanted and texture the way you wanted, then 'shoot' it down…