Mike, clothing is the key.
This weekend I was up in my families vacation home in west virginia, while I was there I tested using my summer bag in winter conditions.
I was under a golite poncho tarp. with a torso ridgerest under my torso and a torso length TARGET blue foam mat under my legs.
I slept in a 45 degree hoodless synthetic sleeping bag in a equinox mumy bivy.
I wore a long sleeve shirt, fleece vest, fleece jacket, and golite wisp wind shirt, fleece hat and gloves, and cotton/polyester, pants and some thin synthetic ski pants. and I forgot to mention some wool socks.
any way there was 2 inches of snow on the ground the night before and a foot the next day, so part of my tarp was burried. the temps were under 15 degrees and I was warm most of the night except for one point when the pad under my legs found its way on top of me, this was easially fixed,but I recomend a full length pad instead of to torso pads.
!!!DANGER!!! I dont really recomend this, I am only able because I am a crazy kid with a high toleration for cold. if I were anyone else, I would probably be in a hospital with hypothermia, but me I was rather comforatable. but with a good layering system, mabey your scouts could get to 15 degrees with a 30 degree bag. good luck :-)