I used to have a DMI cushion hitch, assume the reason he wants to attach the receiver to it is to take advantage of the spring cushioning it provides? 

Somewhere in the dusty, dark recesses of my brain lies a cobweb-covered image of a receiver hitch made to bolt on to a regular draw bar hitch, but I don't know if I am imagining it, or if there was ever one made.

The picture I have was of a receiver with tube stock that slid over the tongue of the hitch, and bolted with the hitch bolt and another drilled bolt hole through the tongue.

Disadvantage of that would be you would not be able to slide the tongue back into the bumper when no using it, so you would comply with the laws that say you cannot have any attachment extending beyond the bumper.

Wouldn't be hard to make, but if the original receiver was still attached to the frame, like comes on most new trucks, I would probably use it.

I bought a cushion hitch that slides into a standard receiver that I really love, it has a hole to pin it like all the others, then rubber on each side so the hitch can slide back and forth an inch or so.  I haven't seen one since I bought it, and I don't remember where I bought it, but I really like it.