I have been looking at ideas to mount a front plate and not drill into the bumper. Here are two great ideas I discovered for BMWs and Miatas. Check them out:

http://www.skenedesign.com/FPBracket/index.htm

http://www.teammiata.com/TM305.htm

We could try to fabricate something similar, or maybe some aftermarket company will develop one for the Challenger.