OK, so you could keep, say, 1/2 or 1 psi on it. Then again, someone in a parallel universe on this forum discussing this very subject.... lol.....said there was no noticeable effect from carbonation on the lagering process. So, may as well go for the service pressure.
Having said all that..... I've seen all kinds of mods on Cornie lids...... one could just take an old one, cut a hole, put in a rubber grommet and an airlock in it.....best of both worlds.