After using this thread a few times, time to pay back the advice received/read.

Flew into Mahon (MAH) this morning. Not a back to back per say, but as good as - having my own Jet2 B757 farewell flight. All non-schengen arrivals have to go through immigration. On the other side of immigration is a flight of stairs down. At the bottom of the stairs there is the landside exit to the right and another flight of stairs up (heading to where schengen flights arrive) and there is a direct "transit" staircase back to the schengen airside.

Timed well it could be a viable B2B but if you arrive with other NS arrivals it might be hairy.