You can use a betting agent with Bitcoin such as AsianConnect88, BetInAsia and others - and deposit your Bitcoin with them and withdraw via Bitcoin with them as well.

They can open for you an account with Orbit Exchange or 9Wickets which are BetFair clones!

This way you would participate, indirectly, in the real BetFair website - and would pay even smaller commissions (3% instead of 5% on the winnings).