Yes, very good idea!

Here's another one I call the "insurance bet"

Take your first selection and back it for a place.

Then take an all-up like this:
1)1st 2nd
2)1st 2nd 3rd
3)1st 2nd 3rd 4th
4)etc
So even if you get half way you make something good to cover your bets and still make a profit!
Mind you, you have to have more bets and split them over three or four all-ups.
But could pay dividends...nothing worse than getting 5 out of six placers and getting BANANA!