Exhaust leak behind engine?

[Brutus]

Just got back from the shop - 3 hr highway drive.
She's back baby!!!
It was the cat. Cleaned it out an voila - all the boost i can stand.
Only problem is for some reason my under hood manual boost controller will not lower the boost so i have full boost all the time - it will go to 15 - 17 and then cuts out. I'm getting a anti boost cut unit or what ever you call it on Monday but that doesn't help me this Saturday at the time attack at Mosport.

Does anyone know of a trick of some kind to lower the boost short term??? I cannot floor the gas because it hits the cut off. It's quite tricky to get maximum boost while staying just under the cut off point.
If anyone could help with this it would be really appriciated.

And the exhaust leak was a loose bolt on the downpipe.