I've been thinking about trying a similar thing. I was going to try cutting out disks, maybe 1" in diameter, at the intersections of a grid, and then gluing them back on to make a pad twice as thick (and hopefully twice as comfortable) without much added weight. it would reduce the insulation value however.
You might want to try using bigger holes. I think they could be much larger than you used without detracting too much from the overall comfort and insulation.