As you said modifying the viewfinder would not be a problem to you (I think of a mask or square lining), I would go that way.
(However take into account that by using a mask you might cut oof part of the rays going to the meter sensor.)
And leave it by that. The hassle involved in modifying film transport should not be outweighed by the savings in film. For enlarging modify the film gate in your enlarger, or mask the film gate in the camera.
Last edited by AgX; 03-06-2013 at 04:37 PM. Click to view previous post history.