No real secret. Either cut the back of the airbox lid off like I did - gets you a big square opening, or get a one inch (25mm) drill bit and drill four holes in the lid wherever you choose - two either side of the central web, two on the sides, up to you really.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball