[PvK]

A clam might be useful before 10 or 20 turns, but that doesn't mean that hoarding clams beyond some limit for 10 or 20 turns would be a good idea if the penalty was going to be a referee making you lose a turn and throwing away your clams and other penalty items and gems. Even if you only lost the clams, it would prevent unlimited hoarding of them.

As for tricks to keep dominion from spreading... I think stone idols and/or skeptics would work, if you are imagining giving them to some sort of referee nation while other nations are inactive for a few turns. It wouldn't need to take many turns if the map were edited so that the referee nation starts with enough (a whole bunch of) amphibious spy units who are modded to be able to teleport on turn 1 (maybe Teleport can be a zero-gem national Water-1 spell for the first few turns).

PvK