PLEASE TRY THIS AT HOME (or, according to my friend Gillian, just buy one at Urban Outfitters)

I've made a mask out of torn cardboard, and taped it in place over 1/2 of the film plane. After shooting the whole roll, I rewind the film in a light-tight bag. I then re-tape the mask over the other 1/2 of the filmplane, re-load and re-shoot. I've simply exposed the top and the bottom of the film separately, allowing for 2 different subjects on each frame that hopefully make one cohesive image.