Can I make exacta and other exotic bets in exchange wagering?

Betfair doesn't currently allow exotic betting on their betting exchange.  The main reason for this is there are simply too many different permutations of exactas, trifectas, doubles and other exotics.  If these were all offered, the exchange liquidity (which is already pretty low until more users start to bet on the exchange) would be split up to such an extent that it would be difficult to match bets.