What about taking the vapor barrier concept one step further and putting the cuben fiber or silnylon stuff sacks many already carry around your feet? Or you could wrap your legs up in your pack liner… but I'd worry about messing that up since I can get somewhat restless at night.
Unfortunately, being from Texas, I have no area to play around with vapor barriers and such. So take this for what it is, merely a suggestion.
EDIT: I almost forgot. I can say that I do like and appreciate vapor barrier layers because I was inadvertently using them long before I ever knew what they were called. I'm actually a huge fan of them for the their cost, weight, and bulk.
At an undisclosed location at an undisclosed time I was issued a winter jacket that some doofus had decided needed hand pockets at the last minute… so they were simply sewn to the shell with no insulation between the pocket and outside world except two layers of nylon. I found that on days when polartech (IIRC) lined gloves weren't enough that 3 or 4 latex gloves between the nylon layers of the outer pocket would insulate my hands very very well. At the time I didn't know why but it worked with lows of about 18 degrees Fahrenheit.