What about betting to show in addition to betting the Money-Back-Win?
If you were right, and the horse contends, you get the show money, but if it finishes 2nd or 3rd, you don't lose $10 on the Win wager, that would normally deduct from a win-show wager. If it wins, you basically get a bonus.
Of course, if the horse fails, you lose the $10 extra bucks.
There are other, more complicated leverage plays, like keying exactly 3rd and 2nd in wagers(trifectas?), but you trade bigger payouts for coverage.
oh just one more thing
= Some races will be negative expectation, even with the bonus (depending on the race itself, and your understanding).