Mark, I've never heard this before about O Sensei. Where have you read or seen this?
I'm pretty sure I've read it. Just don't recall where at the moment. Good bet is from somewhere on Aikido Journal.
As for seen ... I believe there is video of Ueshiba swinging a bokken and switching hands with it. I'm not sure which video it's on though, sorry.
If I run across the references, I'll post them.