A Dremel, a 2.0 inch hole saw, some wire, soldering iron, solder, crazy glue, and a spare ashtray.
It took me 3 hours, but I'm very anal and work slow.
Crazy glue the ashtray shut. Cut out the botom of the ashtray with the Dremel cutting bit. Measure for center (corner to corner), drilled a small pilot hole, then hit it with the hole saw. It will leave just enough material to debur and have a tight pressure fit for a 2 1/16 inch gauge.
Remove the shifter console and trim a little of the ashtray support for the gauge to fit. Spilce your gauge's light into the ashtray's light and route your boost hose the the shifter console. Connect everything and put everything back together. The ashtray gauge holder is supported from the side pressure clips. I still have it. I'll dig it out and post some pics of it.
It is a little difficult to watch while your driving, but once the boost is set, you really don't look at it that much. It is very discrete and some people didn't even notice it while they were in the car.