Instead of focusing on buyers and developers, perhaps the government to consider implement cooling measures for themselves.
One suggest I have for them is for come out with a system where by for land sale, government will award to 2nd highest bidder instead of the highest bidder. This will instantly cause confusion in the market as it is no longer a certainty that developers can win a bid by submitting ridiculously high price.
I know that when developers buy low doesnt mean they will sell low, but I personally think that when market is confused, people will delay their purchase.