All I used to do with unibet 2nd/3rd was back the fav and lay it off on betfair at the closest lay price i could get. It worked a good number of times. At worst i'd lose a couple of dollars due to the price diff on betfair but it was well worth it. I remember Melb Cup last year when Tom W was offering money back to 5th place. I did this along with unibet and another bookmaker and ended up making $400 risk free - it was a fluke though as mu horse came 4th - this was the best possible outcome.