I don't have bar ends on my mountain bike -- which I ride exclusively on trails, so it's a different situation -- but I do have a bum wrist, and I found some grips that work great for me. They provide a platform so that my wrist can't sag. My hand therapist approves =)

http://www.ergon-bike.com/us/grips/

I have the GP1. They're mounted at just the right angle so that they support my wrist in a neutral position.

There are other models that have a small bar end as well as the platform.