If you can get to Trailer Wiring, putting on another connector might be the easiest way to go overall. There's an aux. Turn Signal 'bar' that mounts on the Jeep Spare, and there's another type that mounts into any 2" Receiver. If you've ever needed spare +12 VDC at the Trailer rear, wiring in a 7 pin Bargman has some growth potential via the integral 'Battery +' Pin. Hopkins now makes really slick adapters that plug into Bargmans. One adapts to 4 Pins and other pinout configurations, rectangular or round. Another one at NAPA Auto adapts AND provides a Cig. Lighter Receptacle. Too slick. Nice for a Trouble Light [nocturnal Bike repair?]. I just switched over to all-7 pin Bargmans a few days ago since they're the implicit standard, even if they are overkill for some applications:
http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=bargman+connector+wiring
I especially like their larger Blade/Pin surface area to carry Electric Brake current while providing a more reliable Ground. I always finish off my wiring by packing scraps of dielectric Fiberglass Insulation in both connectors to keep road grime out. Easy to remove.
If you're using a 2" Receiver-mount Bike Rack, as we have from Yakima, I believe there's a neat Receiver gizmo that lets you mount something in the Trailer Bumper [or TV] Receiver and then duplicates the female Receiver a few inches back so you can piggyback Receiver-mount items. You could mount a Receiver turn signal bar in that 2nd, rear-most TD Bumper Receiver. However, you'd still have to wire out a new Connector of some type. Not a bad thing because you then use all standard hardware...
Last, some aux. turn signal above could be stuck on the vertical of the Bike Rack with a major magnet that would hold fast no matter what. This would position the turn signals in the zone where folks expect to see one: ~3' above the ground. You'd skip any hassle this way and have legal, unobstructed rear signals and a redundant stop light.