The attached file is the text of a cr2, that I think does what you want. Use the "OneWay" dial in the Body to xRotate the cube. The set-up consists of 3 valueParm channels in the BODY, and two blocks of slaving code in the xRotate channel of the cube actor.

I have to go to bed now. I'll try to say more about how it works some time in the next 24 hours.