Tohei can be seen on film doing demonstrations of standing on one leg and being pushed. But, did Tohei or his group "assume a one-legged stance and tell" anyone "to come at him"? Not being snide, but interested to know if anyone actually did this. I'd never heard about Tohei's group doing that.
I have never trained with Tohei, but I have training with Koretoshi Maruyama (Tohei's first Chief Instructor of Shin Shin Toitsu Aikido) and yes, I have seen it done; and our group in Guam back in the 70's played around with it as well - of course, not very easy to do - but fun trying