Looks like he's bumping in with the transbrake while coming up on boost. I'm pretty sure he's leaving at a lower boost level so I'm surprised he doesn't bump in then bring it up on boost quickly (since he's probably blowing off the majority of the boost on the line), but I'm not sure how most turbo cars do it (and the Pro 5.0 guys make it easy, but then it's a world of difference with a clutchless lenco setup).