There's a reason customizers throw their spare parts in a box - in case they come up with a perfect use for them later!
For big time GI Joe fans, the comicbooks are where the real story is. The cartoons are fine, but the books are better. And for fans of the comics, there are several important characters who have never been made into action figures. Hard Master was one, Dr. Venom was another, but several remain, including Billy.
Billy, the only son of Cobra Commander, rebelled against his infamous father before he reached his teens, joining the anti-Cobra underground in the Cobra company-town of Springfield. Captured by Cobra and subjected to intense reprogramming, he was used as a pawn in an assassination attempt on his own father. Impressed by Billy's indomitable will and sense of honor, Storm Shadow rescued him and trained him in the ninja arts. Billy lost an eye and a leg due to a missile attack by Scrap-Iron, but Cobra Connader had Crimson Guard Fred III build him a cybernetic prosthetic limb. Billy has also been subjected to numerous "corrective sessions" in the Brainwave Scanner, which have made him over into a loyal Cobra operative, but appearances may be deceiving...
That text was from Billy's filecard, as written by Larry Hama and printed in G.I. Joe #155½, the Free Comicbook Day giveaway. It's not entirely accurate - the Siegie who made the robotic leg for Billy was Fred VII, not III, and it lists his birthplace as Springfield, when that was just a front established after Cobra Commander built Cobra - but it's still the official word on who Billy is.
This figure is born of nothing more than a desire to make use of some of the leftovers from the Professor X custom. This figure is absolutely nothing but James Cameron's Avatar's Jake Sully, with an eyepatch drawn on using a fine-point Sharpie. Mattel's James Cameron's Avatar toys were slightly smaller than 3¾" scale, but that made Jake perfect for a teenager in the GI Joe line. The fact that he was already wearing civilian clothes was a huge help - yes, Billy has a prosthetic leg, but it's not like it should be on display all the time. The kid wears normal pants, you know.
If you don't like Jake's head (or you can't find the variant without the buzzcut), there are several Star Wars figures that could work - Jacen Solo, for instance.