I'll give it a shot. perhaps you could use a half-tone matte and use seperate your image into R-G-B, using the CC tool and then recomp them back via a wipe or mask in Action, to layer each color clip down and as they add together the final color image is created.
Thanks Brian. The screen printing the client means is the kind you use when printing on T shirts. So the effect is more of a painted one. The wipe needs to feel like the image is being painted on but in on clean stroke. Not an easy one I think. Any more tips would be great although we are thinking this might have to be filmed in some way to avoid it looking digital.