It's not hard to work out.

I backed the fav on unibet or the 2nd fav then laid the horse off on betfair for the closest price i could get, then just sit back and wait. It comes 1st - you end up about even, same for 4th or worse. 2nd or 3rd and you're in the money (as you get a refund through unibet, but still win the lay on betfair). It's as simple as that.