The whole point of connecting the emergency breakaway lanyard to something other than the receiver is that the odds of both the receiver and whatever you attached the lanyard to will fall off, at the same time, are small.
On tow vehicles where the receiver is not attached to the bumper it ought to be a viable place to attach the lanyard. It does not take that much force to pull the pin on the breakaway switch that it would tear the bumper off the truck. If it does you've got bigger problems.
You can only plan for so many "what ifs," but you don't have to intentionally defeat one of the safety mechanisms that are already in place to deal with many of those "what ifs."