I know its not what you want, but:
With a 98, you'll likely see little to no gain (other than tricking yourself in to thinking there was some) from the "on-the-car" method. You'd do much better to have torn the UIM/LIM off (20 minutes???) and clean it manually. From there on, you can use the vacuum method every oil change to keep it clean.
Anyway.
You could pull the secondaries back at the spring and zip tie them, or something... (will run rough, I am sure, but you'll be there to hold the TB open to keep it going)
Much better than racing your engine at 4000 rpm..
Ray