Doesn't sound like a good idea to me. Looking at your figures you can either break even, win 50% of your wager or lose 50% of your wager - so to come out ahead in the long run you need the "win" situation to happen more often than the "lose" situation. Lets say on average the true odds of each of the two favoured horses running a place is $1.70 (this is probably being extremely generous given the actual odds in the race you quoted) - this translates to each of these horses having around a 58% chance of running a place. If you work it out this gives the following odds for the 3 overall scenarios (win/lose/draw):
Win (ie. both unplaced) = 18%
Lose (ie. both placed) = 34%
Draw (1 placed) = 48%

So about half the time you will come out even but you will lose almost twice as often as you win - doesn't sound like a winning strategy to me!

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"Computers can do that????" - Homer Simpson