If it's a 6x7 you have, it's perfectly viable to just tape a cable release to the wooden grip. It's something I tried on for an occasion or two. Works fine, though I did move on from that.
Cortisone's very nice, too, (as is topical Advil type stuff you can get in Europe. )
I was just thinking about this when we heard about a member's motorcycle injury, but what I used to use to get under one of those heavy old things might be of use to you: a Vivitar PPG-1. It happens to provide an extra set of batteries to power a 285, (there's an unpowered version, too, but that seems even rarer) but the best of it i you can set it up left or right and to point in about any direction. (In certain of these directions, it even holds a cable release right there for you, too)
With this, you could set up for the left hand. Also get *under* the weight of a large camera.
Or, I'd consider trading you my Mamiya 645/1000s, who has a perfectly wonderful left handed grip.
(No, it wouldn't be fair to you.
But they did make em.)