How great would it be if you could make something like that work!!!
No form, ahh that would be the good life!
What about just backing teh top five regardless? Your still gonna have a high strike rate (80% or so if my memory is correct) , but more likely to make a profit on more races (all you need is a $5 plus winner). Still, I think it would be hard yakka making that work, would need a pretty aggressive staking plan, and then the days where the short priced horses continually get up would pretty destroy you.