I am told (but cannae confirm) that some Regiments sew a softer piece of cloth inside the waistband to drape down over the affected area... it should stay in place nicely and not show as a slip might - unless you need a REALLY long piece of cloth, of course!

The alternative might just be developing some well-placed callouses. I think I'd try the cloth with a basting stitch so you can easily rip it out if you don't like it.