MAN! I guess that you are thinking to complicated.if i can't hide it, i'll try to find a solution for it.
There is such an easy solution. Well ok it isn´t so easy for Vegas, but still easy.
Uhm... what you need is a static not moving bmp you place after the movement of the guys.
So how do I get a "screenshot" or single frame out of Vegas? That´s a good question.
There is something called render image sequence (or in that direction). I currently don´t know were it is (because I have not Vegas on my system), but with this little "tool" you can capture single frames out of your project. A few parameters, an output directory and there you go.
Maybe Ben knows were it is or look at the help files. I think it was in the tools or extra section, but I don´t remeber.