As I was playing a game of Blood Bowl recently it occurred to me that the reroll mechanic could be used as an effective handicap in 40K.
For each reroll to which a player is entitled, once per game, a player could force the reroll of one die. This power could be used even on a die that had already been rerolled due to some other reson (twin-linking,master crafting, etc.), however, a player could not use a second handicap reroll on the same incident if the first handicap reroll did not deliver the desired result. This reroll could be used either to assist the player's army (reroll that missed hit/penetration roll or make a critical armor save) or to hinder the opponent (make him reroll that critical armor save or penetrating hit roll).
Here's how I envision this working. In league play every player would start with a handicap of 0, meaning no rerolls allowed. For every game a player lost, he would get an additional reroll. For every game won, he would lose a reroll. After a few games, the rerolls would result in more balanced games for everyone. Unskilled players or those with less powerful armies would be able to compete with the best.
What do you think?
Edit: I would presume that if both players had a handicap, only the net difference in number of rerolls would be available for the higher handicap player. For example, If I had a handicap of 5 and you had a handicap of 3, I would get 2 rerolls for the game and you would get none.