Its been done i know
 

What about,
selecting four runners
picking one to win,
the others to save...

Pick the shortest to win lets say $100 @ $4
the other three to save

When a loss happens for the top pick add the loss to the savers..

You could use the ratings for free in this site as a test run.
I was thinking more for the Greyhounds as half the feild would be selected.

I know it will/might cost a lot after a few run outs.