This is an easy way to get started in stereo. This set up was seen at the 1993 Eastbourne ISU Congress. The photo more or less explains the whole thing. Apart from the cameras, it appears that the only other materials needed are a block of wood with a locating ledge at the back and on the sides, and four rubber bands.
The ledge behind each camera makes sure that cameras are held parallel to each other ("toe-in" or aiming the cameras inwards is a no-no in stereo photoghraphy). And to change film - well you just remove the rubber bands and proceed as normal for each camera.
To fire the shutters in this set-up, two hands can be used to fire each shutter. Or by choosing an appropriate camera, it may be possible to electronically link them with little or no modification.