The best way to do that is with a plow not a roto tiller. What I have done is either mowed them down and then tilled (back in the olden days when I did that) or just mowed them down and covered them with a thick mulch, and let the soil bacteria work them into the soil for me.

kimmsr,
I've often wondered how to deal with cover crops when one doesn't dig/till. I think you may have answered my question.

Cut the pea and bean stalks at ground level leaving the roots in the ground. Compost the rest of the dead vegetation. You could probably do the same with any cover crop that you grow for nitrogen fixing.