You could randomly select a horse in each race and back it to win and lose 10% over time. This loss could be reduced by getting the best odds available, but 10% is a nice figure to use as a starting point.

To reduce your losses you could eliminate any horse that opens longer than pre-post. Do you own Due Diligence but the failure rate of horses opening longer than pre-post is astounding.

You could also eliminate horses that start at 50's or longer.

You could also eliminate horses that have a high Win S/Rate in Group 2 events and higher.

The above suggestions, I believe, would put you in profit.

Add the overbet factor of popular horses in leading stables and the list of things other than form that will tip the odds in your favour goes on.