I'd much rather have this than a loose cord sticking out the back.
You could run the cable out of a drilled or dremeled spot right beside the normal controller cable. Seriously, it would look worlds better, and hold up a lot longer then just smearing hot glue all over a small external box thing you patched together. You clearly have skills for doing the soldering work, so there is no excuse to just ignore the fact that you could make it look worlds nicer if you took the time. It pays to go the distance.
Also, and granted you are probably not selling this one, but you need to keep in mind that many people are allergic to the chemicals in hot glue, like polyethylene glycol, so you want to expose people as little as possible to hot glue on any end product/project you sell or give away. A lot of people don't even know they are allergic to it until their first exposure. Just friendly advice from someone who has been doing this kind of stuff for over 16 years. Hot glue is meant as a product to be used internally as much as possible when electronics are concerned, or for items that will not be handled often like woodwork and crafts that sit on display.