This could be a winner - help wanted!!!

Hello,

I am looking for help developing a trigger for the following strategy;

Using level staking - ie; 10% of bank on each event

I would like to bet using the following criteria;

SP Odds of favourite                          bet equal amount on first
3 to 4                                                 2 horses (ie. 1st & 2nd fav.)
4 to 5                                                 3 horses (1st 2nd and 3rd etc. ...)
5 to 6                                                 4 horses
6 to 7                                                 5 horses
7 to 8                                                 6 horses

Much Thanks