I don't have pictures yet, so bear with me. Edit- Pictures!
Construction time- 5 minutes (not even)
Materials- Duct tape, string, hole punch / puncture device, dirt / sand
Take a piece of duct tape, say 5-6ish inches long, and lay it on a flat surface. Take another piece of duct tape of the same length and stick it to the first piece on the edge, so the two piece make half a square. Now, bring the two separate ends together at the other end as if they were going to make half a square. You now (hopefully, have a pouch!). Cover the stick side of the tape with dirt / sand/ substance that will remove the stickiness, so the tape won't stick to itself, etc, running your pouch. At this point, fold the corners down inside a bit, and take a hole punch / knife / puncture device to make a hole at either end where the two pieces come together (or at your folded down bit). Thread some cord of any type through the holes, tie one end outside the hole, and make whatever release cord and finger loop cord ya want.
I think I'll use this sling for my hobby idea, because it really is quite easy to make, and it'll get em started.
If could, please try this and test it now, and give feedback, I think it works, but more advice from others slingers is wonderful!