I had an almost identical break to the one you have posted.
I had my cast of 3 weeks ago and the hospital offered me bugger all in the way of physio, they just gave me a little brace and said keep it moving.
This weekend was my first proper ride where I felt I could go fast and hard downhill again.
Like has been said the worst part by far is getting the tendons moving again that have not moved for 6weeks+.
I bought one of those spinning gyro balls to strengthen my wrist, and just kept using it. The first small couple of ride it was horrible and hurt a lot, but then after a bath it felt better for it… you just got to use it.