When tech trading is off, how about all races have a mega event and gain the alliance tech after a certain amount of turns have based?
Its odd but for me tech trading has always been one of the most interesting concepts in a strategy game, all the way back to MOO2 multiplayer on small maps. A friend sitting next to me would declare war on an easy opponent and all of sudden his face would drop as he realised what technology they now had facing him

. The only trick was to make sure I drew the war out as long as possible and not make things too unbalanced for either opponent.
Fun times, its no less true in Galciv, feeding minor races tech and ships for your proxy wars and cackling evilly.