What kind of gear, and do you mean that the "back" of the side pouches is the area between the 2 zips, that will be sandwiched between the pouch and the parent pack, or do you mean on the outside, away from the pack?
I added some 1" webbing, like individual PALS points, on the outside of my PLCE side pockets, then mounted compatible pouches to those. Didn't do it for when the PLCE pouches were mounted on the main pack though, because that would have made the whole assembly wide and ungainly. I wanted to use a Kifaru Organiser to mate two PLCE pouches together better as a day bag.
A regular home sewing machine managed it, albeit with regular SewAll thread, not heavy duty pack thread.