Forearm stuff -- assuming the stress is mostly coming from gripping and stabilizing your wrists:

Wrist curls and reverse curls
More fun: wrist roller!

If you've got a kettlebell, bottoms-up clean-and-press; kettlebells in general are great for grip strength and wrist stability.

If the strain is hitting your elbows as well, scroll down further in the linked entry for a couple of exercises I've found useful for warding off elbow tendonitis from climbing.