There is a system for mounting the can to the side that doesn't require any drilling and looks pretty well engineered. Can't remember the company that offers it - might be morryde. If you have the stock tire carrier I wouldn't recommend adding the weight of a gas can to it without any reinforcement. There are several options for reinforcing your tailgate/tire carrier that include mounts for jerry cans. You could always go that route and keep your bumper.
07 Jeep Green Rubi Unlimited, auto
Mods: Tuffy Cubby Storage Cover, Rugged Ridge grab handles, Shrockworks Sliders, Rock Hard Engine / Gas Tank Skids, Rhino-lined tub, Kilby Evap Can Relocation Kit, 16x8 Centerline Wilderness Series - Falcon Rims, 285/75/16 Interco SSRs, OME 2" HD Lift, PSC Diff Covers, Superwinch EPi 9.0, BulldogFab Rear Bumper, RedrockFab Front Bumper and skid