Good write up. I opted to tap into the ECU MAP line closer to the ECU. Doing so placed the plastic "T" in the air plenum instead in plain sight. I did this for cosmetic reasons.
The hose is tee'd near the ECU, then travels under the plenum to the drivers side. From there, it exits the plenum briefly then enters into the cabin via a grommet very similar to what you have chosen. In the end, you cannot see any evidence of a gauge install other than what's in the cabin.