Rock 'n Roll!
About what to do to help stop your legs from falling asleep: I was in Japan a coupla years ago and we had to sit in seiza for a long time while my dojo group was being graded. The Japanese chief examiner sat in seiza for more that an hour during that grading. When we were given a few minutes break to stretch our legs, we were all hobbling about like old men but all he did was to raise himself off his feet and rock backwards and forwards a few times on his knees before sinking down again into seiza and waiting for our return!
I've tried it and it does help a little. Let us know how you find it.