There is only one move I can think of in our kata that has only one hand on the bo. I think it is Sushi no kon (forgive the spelling and I might have the kata name mixed up as well). It is a one armed block, of the rear leg, in long stance. Of course, one is using one's body/frame and arm for stability. But frankly, I'd be scr*wed...because that is a really weak stance/technique with me.

Cardinal rule: both hands on the bo at all times.