Quote Originally Posted by Paul Sorensen
My Mamiya 645 super does this. It has a simple double exposure switch which remains on until you turn it back off. With the winder you will not need to remove it from your eye, if you are winding it by hand, that might be a different story, but theoretically, you could do it.
Same with M645 & 1000s. I think it is missing on the cheaper (J?) version.