Only way I can see it would reduce lag steve is if you had one very small turbo (that would spool up virtually from idle but run out of puff say at 3k rpm, and it blew directly into a second turbo, a much larger one that wouldn't normally come on boost till say 4k.... So you would use the exhaust gasses to spool up the tiny turbo, and that tiny turbo is what would spool up the big turbo and thre big turbo feeds directly into the throttle butterfy.................???