I use aerobars for this very problem. Having tried a multitude of bars and countless hand positions the only thing that offers me relief from the pain is to get into the aerobars and totally take the weight off my wrists.
I find that about 5 minutes in the aerobars every 30 - 45 minutes riding as a minimum, and the pain stays away.
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"Surely one can love his own country without becoming hopelessly lost in an all-consuming flame of narrow-minded nationalism" - Fred Birchmore