[dagnabbitt]

I guess I don't know what you mean by "hidden"... or rather how hidden it needs to be. I have a standard, regular old off-the-shelf hitch on my 72 GMC 2500 that goes under the bumper. I think that they are easy to get.

I also coincidentally have exactly what it sounds like you are looking for, something that goes where the license plate goes. I don't have any pics of that but the previous owner of this dock bumper took a standard hitch and modified it in such a way that it is higher than standard. He put a hitch-sized hole in the license plate so you could use it that way. I haven't looked at the welds to see if I would trust it, but it might be the way to go: get a standard one and then cut and weld.