I built one where the east-west stitches of the belt loop ran between the north-south stitches on the edges of the pouch. I just kept the loop from going all the way to the edge. To attach the center of the pouch front and back I used one rivet in the center and one at the top, I dont remember but imagine I just put the rivet setter anvil between the loop and back of the belt. Sew the loop, then the sides, then rivet. Unfortunately I dont have pictures, I decided a double pouch was too big for what I wanted and cut it in half. As a double mag pouch it worked well though.
Another I did, better I think and will work for you. It's a single, but will double easily, just seperate your belt loop on the back into two loops, one behind each magazine. You can see I found a use for those belt ends that get trimmed off. If you ignore the bad stitching (one of my first pieces), the style is serviceable and easy.