Set the pressures using temperature - it should be around 80 degrees in use (realistically with an IR sensor and after bringing the car in you'll only see 30-40 though), with a ~10-15 degree split across the tyre, with the inside edge being hotter (example: inside edge 40, middle 35, outer edge 30). The centre of the tread should ideally be bang inbetween the inner and outer edge. Tweak pressures until this is the case.
Sounds like you have been underinflating the tyres a lot at the moment, and more pressure should help support the tyre and reduce the outside edge wear.
You might need to soften the car up now though, as more air in the tyres will add rate to the (already looking pretty stiff IMO) suspension system...