I dont drive a JK, but when i took the caps off my XJ I just left it as is. For that price, for what you gain, id do the same.. No one is gonna come up to your Jeep in the safeway parking lot and say HOLY HELL THATS UGLY WITH NO CAPS MATE!
Use a square, and cut it off straight up an down and leave it till you get the bumper you want
looks fine with no caps
Plus, once you take it out to Mclean an run up the crack, you will probably find you come out of there with no caps anyways