I'm against drilling any holes in a kettle. Can't bring myself to do it. After a lot of back and forth with
@Jules V. this is the solution I came up with for my Performer:
The best part is nothing needs to be permanently modified on either the kettle or the Billows (assuming you have a propane assist burner tube). Just pull the hose, slide the billows on, and go.
The parts needed to do this are the Universal adapter from Thermoworks:
https://photos.smugmug.com/photos/i-KWnjNc2/0/a888be3e/XL/i-KWnjNc2-XL.jpgRound SS tubing from McMaster:
https://www.mcmaster.com/1750T13/and some JB Weld to join the two together. The tubing is a nice slip fit over the 3/4" O.D. burner tube. If you want to use the propane assist feature you just pop the hose back in the burner tube. I removed the circlip holding it in place.
I tried it out last night on my riser setup without a heat deflector by setting it to 325, closing the bottom vents and closing the top almost all the way. It crept up to 322 before I had to start flipping the flank steak.