A good start would be extending the Expert's skill points to 8 + Int modifier, as a Rogue.
Bonus skill-related feats make sense. Experts should always have access to Knowledge (all). (As far as I am concerned, Knowledge should be a class skill for all classes, but that's another story) Experts should not be deadly in combat, but their low BAB and hit points, plus lack of combat special abilities, is enough to keep them out of combat-- it could still be balanced to allow them to pick their feats from any feat they meet the prerequisites for. Other classes might take levels in Expert for this ability, but remember that it weakens them in their primary class abilities.
A level based bonus to all Knowledge skill checks would be nice for the Expert as well, and access to a class ability like Bardic Knowledge.
As a side note, I have been trying to figure out how to improve the Aristocrat into a fully playable PC class. I'm thinking that giving them the Psychic Warrior's bonus feat progression, replacing Weapon Specialization at 6th with Leadership, would be enough to make them able to keep up with the regular PCs. Their bonus feats should apply to the Fighter bonus feat list and possibly some nobility or social-based feats.