My previous trainer had me do a protocol he called "Billy big boy grip strength". I have not found it discussed anywhere else but it worked a treat. But definitely keeps wrists fixed.
He had me work out how long I could dead hang for and then at the end of every workout session he would have me dead hang for 1 quarter of my max hang time every minute on the minute for 8 minutes. He said I could do this after every session no stress. I would increase the time regularly. I stopped doing them when my grip strength caught up to my deadlift (the lift I was having grip troubles with).
The timing is probably not feasible if you dead hang for more than say 2 minutes, but I would suggest this is more a beginner protocol than an advanced protocol. If you can dead hang more than 2 minutes then I would be surprised your grip is holding back your bench. Maybe in that case work on your deadlift as one of the other posters suggested.