So one of the players bough a Charron pattern light battle servitor with the heavy stubber, in the near future I predict that he will want to upgrade it some. Weapons and additional bionics is easy. As is extra skills and talents (given the rules from Inquisitors Handbook), but how should one approach the subject of raising a servitors characteristics?

There was a lovely supplement on Dark Reign which basically you "built" a Servitor like a character, only instead of EXP you spent Thrones to upgrade it. Not sure how that would work in RT where you don't exactly keep track of Thrones. I think they took it down due to IP reasons, but it might be out there somewhere still.