wow, they won't let you even get GAS without a plate visible?
Mav's ideas are good, and I'd think either using a plate holder and fabbing it up somehow might work like that, or else if you can hit a junkyard and look around for one off another vehicle that might work too.
Another possible idea here is: If you have a spare/old plate from something else.....screw or bolt THAT through the front bumper or something somehow...probably using the bottom holes on the plate. Then use the top holes to "mount" the proper plate to the other one. This essentially makes the "old" plate a holder, and you just deal with the two other holes for holding it to the holder. I know...sounds like extra work, as you could just screw or bolt the plate down directly, but if it might work, it's an idea. The guy who had my '80 J10 did that on the rear, which actually works well, since the lower bolt holes are down along the base, and with the hitch ball there it's hard there it's not as easy to deal with the proper holes. By just mounting it to the "holder plate" it works slick. Anyway, it's just an idea in case you, or anyone, can use it.