Hinging the pad: I did this for one of my kids, after reading about it here. First, trimmed the pad to equivalent of 3/4 length for her height, rounding corners and tapering like a Prolite. Then cut crosswise into three pieces, and taped back together with 2" clear packing tape, so that the two cuts would hinge on opposite sides and the whole thing would fold like a "z." Taped both sides of the hinge, 'tho of course, one side had to be taped with the pad folded. Worked fine--certainly durable enough for a few days, and prob. a lot longer.
I think the folded pad measured about 20" X 12" X 1.5" made out of 1/2" CCF. Packed against the back of the pack, so it makes a bit of a frame. I don't know if this is any more compact than the "burrito" method lots of people use for CCF.