By yourself some carpet thread and a strong needle and have at it! It is a lot easier then you think.
I have modified all my packs this way. Some just a "D" ring with strap. A "D" clip shoulder attach point for my GPS. I added a meat flap/seat flap with cinch buckles on one. My X2, I put an upper rifle sinch strap so I could put my rifle butt in the side pocket and sinch down the barrel so I could have "hands free" when I needed, or on the hike out in dark. A knife attach point, and a leather man attach point. I use the smaller Zip Ties as a Molle attach Tie allot as well. They work great in a "X" pattern on Molle loops.