It's possible to build ANYTHING you want from scratch, if you have the capabilities and equipment. You think the first ones grew on trees?
I've built a lot of Stens, still got a shelf full of kits from back when they were 3/$100. If you were desperate enough you could probably adapt a Glock mag to a Sten by cutting the grip off a Glock, removing the magwell from a Sten, and attaching the Glock grip to the Sten tube with a couple of brackets. You may have to modify the pick-up ridges on the bolt to accommodate the Glock mag, been a while since I messed with one and don't remember exactly what they looked like and how wide they were.
You could always make a new sheet metal Glock magwell to replace the Sten magwell. It's just attached with a couple of spot welds.