One thing I have found when looking to create lay systems, is the answer is can sometimes be the opposite of what you think.

In this case with jockey trainer SR's, the answer could actually be looking for the combinations with the highest strike rate. Yes they are going to win more often, but hopefuly they are overbet, and therfore value for lay betting.

This may not turn out to be the case with this method, its not something I have looked into before, but as a a general rule of thumb for me, is I look for stats that make a horse look favourable as a win betting proposition, and often find that so do most other punters, and therefore there is no value in backing them, however laynig them can be a goldmine. Most of mylay systems are based on ideas such as placed last start, good barriers etc etc.

Just a thought anyway.

Good luck!