I think you're on the right track,.

You could back your sizing die off so you aren't sizing the entire neck down but are leaving a false neck just in front of the case shoulder, to keep the case seated tight against the bolt face and then fire form the brass.

Once formed to fill your chamber, only bump the shoulder back a couple thou when reloading and you'll be good to go.

Last edited by colodog; 09/18/17. Reason: complete sentence...
"Camping places fix themselves in your mind as if you had spent long periods of your life in them.
You will remember a curve of your wagon track in the grass of the plain like the features of a friend."
Isak Dinesen