I personally have not had this issue that often, but being the "big guy" in training definitely makes things difficult.
Getting technical is easier for smaller guys mainly due to the fact that they LOSE when they make mistakes.
Bigger guys can begin to rely on strength when they make mistakes and often times can get away with them.
Other than bringing in other big guys to train, I think the best way for a big grappler to improve the fastest is for him to study the way an elite grappler (that is also big) moves from all positions starting from the guard.
Then the next step is to throw away the ego, and roll with everyone in class without using strength.
Believe it or not, a big guy with a developed guard is one of the most difficult things to deal with.
and now here is a Roger Gracie highlight. Probably the greatest heavy/big grappler of all time.