I have an old Golite Pinnacle that had very small pockets. My DIY solution involved sewing on two small bits of webbing that hung down an inch below the waist belt. The webbing ended in a 1" common loop---a small square plastic loop. They were spaced to match the column spacing of a MOLLE pouch. I used Malice Clips from Tactical Tailor to attach a pouch to the loops. I can still use the original pocket on the hip belt, and hanging below, is a pouch large enough for my sunglasses, sunscreen, maps and a snack. If I choose to remove the pouch, the webbing loops are hardly noticeable. As you noted, MOLLE pouches usually aren't the lightest solution, but it works well enough for me that I don't mind the extra couple of ounces. If you shop around, you can find lighter pouches made of 330d or 500d cordura too.