Triptychs

Anyone have any snazzy ideas for prtinting triptychs on a single sheet of paper (as opposed to mounting separate sheets in window mounts)? Is it easiest to create a mask and just do sequential exposures or does someone have a simpler trick? Thanks.

I would just mask it. Even neater, and I'm not sure how to do it, would be to have a part of each picture flow into the one alongside.