I feel sure that if you want to bad enough,,, you will get it in. Many, many years ago, when i wore a younger mans clothes. My new wife got very turned on and would cumm really hard when i stretched her. We had never heard of fisting and there were on movies about it. But i kept trying to stretch her more each time. After about a year of this almost nightly during one of our trys,,, my hand went in. She screamed and had an intense climax and almost passed out. Wa,,la,, all the trying was worth it. Sooo, keep trying. If you want it enough it will happen.
I agree. The head of a hitachi isn't all that big. I'm actually surprised it isn't used for penetration more often. I don't think I've seen it done in porn more than maybe once of twice. Would be crazy hot to both see and do I would think.