I had one of this companies in-vent boost gauges in my old BMW 335i and it was great. Looked factory fitted and was super reliable.
http://www.p3cars.com/
They don't have one for the G as yet but with sufficient interest they would be able to get something into the works.
So is there anyone interested?
Why, what for?
The GQV already has a boost gauge (bar chart) displayed on the dash when in "D"
Bar chart on dash is pretty useless, the in vent gauge can also display a heap of other data to assist with tuning etc.