Below are the pictures associated with the (to my knowlwdge) FIRST EVER POST-FACTORY PRIX HUD install.
Click to go to ClubGP where I wrote my how-to write-up.

The items that you'll need. HUD unit, dash piece, and switch. Wire with plug in from unit and switch, along with two bolts, and I used 5/18 thermostat wire. It was inexpensive and kept it organized.

Behind the instrument cluster is where I cut out a bigger hole so that I could get my fat hand where I needed to go.

I removed the clips from the dash piece and used chalk to trace the outline edge where to not exceed in my cutting. Remove the clips to make it easier to put into place and double, triple check that your staying where you should be. Chalk was easily seen and removable. Marker might be visible after complete and pencil didn't show up well.

The point of no return. Using a dremel type tool with cut off wheel to get through the soft layer. After this, I used a bit type grinder to get through the had plastic layer.

The display unit in the new hole.

I couldn't get the HUD made center counsel from my parts car and a new one was too much, so this is where I mounted the switch. Far enough ahead to move the seat all the way forward. But still within reach for something you don't touch/adjust often. With this write up you could mount the switch almost anywhere.