I understand. Made me think, I pulled out my Grand Trunk UL hammock, and it's the same measurments as your uqp, 106" long, and about 60" wide(), so I pulled out my hammock and strung uo the GT underneath and it actually fits quite nice. With my full length 20* uq on, the GT came about about halfway on both ends of my BMBH.
I'm thinking, keep the shock cord, but add loops to the corners to attach your hardware of choice(ie. hook, carabiner, etc.), that way, you could attach the corners to the corners of the hammock, yet still cinch to fit eaches hammock and quilt size. That way you can make just one uqp for all quilts, cinch tight for the gathered-end, loosen up and use corner loops for bridge style, best of both worlds...