I use a 20x 20 x 3/8 pad folded over to 10 x 20 (2 in cold weatrher) as the frame for my pack and under my legs/feet in the foot box of the WBBB. Problem is they won't stay put even if between the bottom layers. Think I'll try Cannibals idea and use my pack w/my feet thru the hip belt. Sounds clumsy but might do the trick.
Any other ideas for keeping the foot/leg pads in place?