I have considered doing such a thing. Having a race that is nothing but trouble for others, and no I don't mean being naturally aggresive
How about agreeing to trade ships and then scrapping your ship in the turn the other empire expectedly agrees? I can't help but expect this sort of thing, in a current game the other guy gave me some colony ships, pity they are something like 6 months away from my nearest ship yard. Still it gives me time to withhold my end.... I mean make them available.
I am cursed with the ability to figure out all these exploits but I can't bring myself to do any of them. There's a point where being sneaky turns into outright unsportsmanship.