This may seem like an odd question, but how thick is the back padding on your pack? If it's within the same range as the pad you were thinking about taking anyway, well...
41 isn't that cold (at least, it isn't for me); I think I'd be able to get away with using my pack (which doesn't have any padding along the back; it's just two layers of 1000d Cordura) as a pad for my legs as long as I had long sleeping pants and decent socks (which are something I'd carry anyway for trips below 50 F). Note, though, that I'm a particularly warm sleeper.
Anyway, it's just a thought.