I had been doing the frog stand for a while and was trying to do the tuck planche when I ran into a problem... my wrists aren't flexible enough. (As an aside, it showed me my arms were too vertical in the frog stand.)
Lying my forearm flat on a table, I can bring my hand up to about a 60º angle. With my hand flat and bringing my arm up, I can get to 90º before it becomes painful.
What is the best way to improve flexibility in my wrists so I can progress in this exercise?