I have looked, but never found a solution for this other than buying one of the few portable grills out there that are made to be plugged into the quick connect low pressure. CruiserRV (and probably all other brands as well) sells such a grill as an option when you buy a new trailer. They also come with a rack so the grill can attach to the side of the trailer above the quick connect. These grills are usually much more expensive than the typical ones that use the small green bottles. The challenge is how to connect a hose to the grill. Most portable propane grills have a regulator with an integrated dial for turning the flame up, down and off making it a difficult plumbing job to bypass. I just refill my own little green bottles and don't bother with the hose connection problem.
I do have a spiffy portable fire pit with a 12' hose that I plug into the trailer side quick connect. We are using it more and more now that many campgrounds have fire restrictions here in SoCal.