If you could keep it in the neck, or use it in a straight walled case, a simple gas seal would work (if you used a suitable plastic). Like the old Alcan PGS, a cup face (hollow) down seated, and then seat the boolit on top of it. It would stop gas cutting, but sufficient lube to stop friction leading would still be needed.
Alternatively, how about cups like the Hornady (If I'm right) nyclad jackets that cover the bore riding part of the boolit?