Boosting in private matches

[theadvncd1]

Just had a question about boosting in private matches. It says you can do so in the achievement guide I have the game for pc and xbox and two different gamer tags (mine and my brothers) can I sign one in on the xbox and one on the pc and make private matches and boost stuff like the ones that require 100 kills with different weapons kill 100 of the different races ect??