They make O2 sensor simulators that wire directly to your sensor wires. These are made to send a normal 02 sensor signal to your engine's computer to turn off the check engine light and make it run normally. When I put in my new exhaust I originally left out the O2 sensor and purchased one of the simulators ($30). They work fine driving around town, but when you take them on the highway and put some load on your engine for an extended period of time, the thing will get all messed up and your car will run like crap. I ended up taking it out and installing an O2 sensor. As far as I know, one of those simulators is the only way to bypass the O2 sensor without a catalytic converter. If you just use your Jeep for driving around town, then I guess one would work, but I would recommend installing a catalytic converter and O2 sensor. You can buy universal hi-flow cats on eBay for pretty cheap (not much more than a sensor simulator).
2000 TJ, 2.5L, 31" x 10.5" muds, 2" Pro Comp lift, JKS Discos, 1.25" wheel spacers, ARB Safari Snorkel, hi-flow cat, dynomax cat-back, Accel Super-Stock wires, electric fan, safari roof rack