Since I usually play Point Buy, I might alter the Construct ability score adjustments by simply saying "You start out with 5 fewer points than organic characters, and you have a Charisma modifier of -4." The -5 is to make up for you not having to put points in Con, and the -4 is still hefty, but can be overcome, so that somebody who really really wanted to make a Cha10 "Diplomatic Servitor"-bot or something could do so without trouble.