I put one of these on my Wrangler last week: Surco BT300 Spare Tire Mount Bike Rack, Up To 3 Bike Capacity : Amazon.com : Automotive

I am not a fan of the clamp to hold the bikes on... you need to un-do the whole thing to get multiple bikes out. BUT... it's cheaper than Thule / Yakima + it goes on and off very slick. Highly recommended for those with outboard spares.