The only other choice is to have a long cord or an extension and drape the cord over your tailgate.
My 2015 2500HD had the wiring harness tied up right behind the rear license plate. The end of the harness is just the wires wrapped in shrink tubing. The only part you have to purchase is the connector. I did this job myself in 45 minutes. It's pretty easy if you have the right size hole saw and 4 self tapping screws along with some electrical knowledge.
2015 Chevy Silverado 2500HD CC Duramax
2016 Eagle 323LKTS Java
Pull Rite SuperGlide #4100 Hitch w/Mor-Ryde Pin Box