You should be able to do this yourself. All you have to do is T into the pressure line on the intake manifold and run that line into the cabin. You will then mount it to the gauge. You should be able to find a gauge online or in a performance Magazine.
Be sure to get a lower boost gauge, the D will only produce about 7-10 psi at max levels. A 30 psi gauge will not be good for your application. I would go with a 15 max.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS