What pants do you wear?
If I wear pants with thick waist material or belt loops, they tend to give me a similar problem. It also occurs if the pant drop lower than the pack belt.
I solved my problem with running shorts or mountain hardware pants that have the integrated belt.
I'm with you and wouldn't use a maxi pad as anything except a short-term solution. They do not hold up to a lot of friction and sweat and can cause terrible chafing. The edges of a pad are no different than having a pant seam next to your skin.
Body Glide is great stuff and might help.
Would an aftermarket seat belt cover fit? Otherwise I'd buy a cheap life preserver, some sort of closed cell foam covered by that nylon fabric. Chop it up and find some way to sew it into a sleeve to go over the hip belt, or otherwise attach it.