There's a number of ways of doing it.
I took the vacuum actuator off (the black thing on the side of the pipe), opened it up (carefully because the plastic tabs are brittle), then put some 100MPH tape over the hole leading to the pipe.
This makes it externally undetectable and easy to reverse.
The trickiest bit was working out that the actuator needs to slide "up" towards the bottom of the car to be removed.
There is a German PDF that explains it, but is 3MB (and, of course in German).
PM me with your email addy and I can send it to you.