well, you could always let ships pass though, but not able to attack each other. like a forced peace treaty.
actually, i just thought of something:
atm, when you have a peace treaty, you have to officially break it and tell the guy you intend to stab him in the back etc etc
so what happens, is you break the treaty, but you cant attack for i think its 2 minutes or 1:30, then when times up its fair game.
so, in a game with a forced non-hostility timer, IC could just use that existing function, except set the time to be whatever the player chose before starting and set it so the peace treaty ends (i.e. the countdown timer starts) as soon as the game does.
if that doesnt work (i was just thinking for that split second at the beginning of the game where the players are allied. it could show everyone where everyone elses homeworld is...) so if that doesnt work, the Akkan has an ability to force all ships within the ability radius to cease firing, but become invulnerable. so, if the same effect could be applied to each teams ships but without the invulnerability bit, then it could achieve the same affect
in terms of the ships thing, well, like i said, you can let them in your systems but they (nor you) will be able to fire. until the time is up and you can always put a scout in all your border worlds to give advanced warning of a player trying to sneak up on you