Sure, Hoot, and this is how one can check focusing accuracy of the rangefinder... Use a magnifying glass to examine a translucent focusing screen at the film plane and see if the subject is in focus both there and in the rangfinder/viewfinder. Some people have used an actual SLR ground glass screen placed against the film plane with the matte surface towards the lens, so that the "ground" surface is exactly where the film surface would be. A much cheaper cruder but workable option is to stretch several lengths of that frosted type of Scotch tape across the film plane for the test.
Out in the field, the actual ground glass would be more convenient by far, but still quite inconvenient considering the camera must be empty at the time. 120/220 film can't readily be rewound like 35mm can. So you'd finish a roll, then have an opportunity to use the ground glass, then load a roll and shoot the whole roll before being able to place the ground glass again! Still, that does give you a parallax-free 100% view of what you will get on film (noting it's a rare SLR that gives you 100% in the viewfinder), also including depth of field.
And if this were a popular thing to do, someone would build a gizmo similar to the chimney kind of waist-level SLR viewfinder to snap into place over the film plane. Indeed I think such a thing IS made for 4x5 cameras. A right-side up unreversed view would be nice.
Thinking 4x5 still, I can just imagine getting lined up on one's landscape scene this way, and then inserting a film holder without even needing to disturb the viewer gizmo. Pull the dark slide, signal to your lovely nymph model to cavort gracefully across the sward, and press the shutter release! One could even take several similar exposures without resorting to the viewer... Classic fun!
