DynaLite has an optical snoot that I believe will help solve your problem if you have $1200 to spare. I have been considering one of these to power through some of the washing issues that I have had with the setup below.
I use a 750w ETC Source 4 spot for back drops.
You have to be very careful with light spill onto the back ground or the forward lights will wash any effect that you are going for. A grid on a soft box and placement of the light sources to the side of the subject helps, but you still have to essentially shoot for the effect you are trying to accomplish with the projected image. I shot a quick example without the grids on the soft boxes.
Sorry about the model:
On the left is the setup pictured with strobes triggered to show wash pattern. On the right is the slightly over exposed me as a stand-in. In the middle is the same effect using the modeling lamps as hot lights and a VERY slow shutter speed 1/20th. I have some new 1000w hot lights that I havenít setup yet. Maybe if I get an attractive model in soon I can post an example.
The optical snoot is looking like a "cool" alternative to the hot light venture!