I found that using basic techniques like "no coasting" (always on the gas or brakes, somtimes both) helps keep boost up. The only other tidbit I can offer is to anticipate when you'll need power and apply it a fraction of a second early so boost will be there.
After running the WRX last summer at a couple of events including the autox school I was surprised at how good it is in stock form for autox'ing. The biggest weakness that I found is the brakes (I was running 17's too) which get soft after a few hard applications/ left foot corners. For anyone looking to get serious, stainless lines, upgraded pads and fluid are a must-have for every class but stock.
As for Jake, he kicked my butt several times last summer. If you can emulate him, you should be driving professionally