RattyMouse: As others have said, if you want more open shadows and lower contrast you need more exposure and less development. That would be the easiest way. Having said that - the "10%" you are after is very small and can likely be tweaked out of your printing/scanning without adjusting your film exposure/development.
If you want to maximize the amount of film speed for your shadows and lower overall contrast you can also try diluting your developer more, extending development time and increasing the amount of time between agitation intervals. This would take some experimentation though. A naturally compensating developer does the same thing.