A simple trapeeze arrangement that allows the photographer to hang upside down by his knees behind the camera would do the trick.
I hope you guys don't try to steal this idea before my patent comes through.

Sinar has/had a reflex finder for their 4x5 F. I thought it was kind of useless. You don't need it for shade in the studio and you have to remove it to critically focus with a loupe. As far as inverting the image, it makes absolutely no difference to me at all. My brain does that for free. The only time I notice it is when someone looks over my shoulder and says "Hey, it's upside down!"