Sorry didn't see thris thread earlier so probably a bit late to answer now.

I agree with Benni, its an awkward exercise that hits a couple of muscle groups so you would be better trying more specific movements. Side Raises and front raises maybe?

I was also going to suggest using an EZ bar as it takes some of the twisting off the wrists but you've already covered that. better than a straight bar though. I just think due to the unnatural movement its not the sort of exercise you can go heavy on. Maybe go slightly lighter and try drop setting it?

Oh, I've just had an idea!!! Do it on a cable machine with a rope. The rope with knots on the ends that you would usually use for tricep pulldowns, reverse that movement and use the cable pull at the bottom of the machine. That should allow you ample movement in your wrists to take the strain away from them.