I came along this nice strategy in a recent multiplayer game, I would think it's been done, but just in case:
Player 1 builds leonardo's workshop, turn goes by everything upgrades
Player 1 donates leonardo's workship city to the other player
turn goes by, they upgrade
Player 2 donates city back
should only do this if you trust the guy
Player 1 builds leonardo's workshop, turn goes by everything upgrades
Player 1 donates leonardo's workship city to the other player
turn goes by, they upgrade
Player 2 donates city back
should only do this if you trust the guy