You might like to try wrist pushups. In one dojo I visited, they rest their wrists on the tatami, palm up, with fingers pointing at each other. Then they do x pushups using the wrist for support. Then, they rotate the palms outwards, so that the fingers are pointing away from each other. And then they do another x pushups.
Don't know about you, but this was the hardest part of the warm-up for me