Oh cool! That is not at all what I thought you were talking about, but that is super sweet.
Btw there was some issue with your link. I think the "!!" fell off the end of the link. Here is a working one.
http://www.bikepacking.net/forum/diy-make-your-own-gear-(myog)/pack-girdle-to-deal-with-those-bulky-items!!/I don't quite have clearance for the full tent all rolled up to slide under my seat bag, but I definitely could fit it if I folded the tent flat, perhaps folding it around something like a flexible cutting board, or whatever that material is they use to stiffen bikepacking bags. Then I could wrap it in my tyvek groundcloth to keep it dryish and to keep the road grit off it.