Simply give everyone $50 to bet with on Group 1 races just as we have been doing, but only $30 for Group 2 races and $20 for Group 3 races. Something like that.

You could go straight out if you wish, but in feature races you often get short priced favourites. Betting each way gives people more confidence to pick away from the fav in these races knowing they can still pick up a nice place div if the fav wins.