Way back when, I has installed a wiring passthrough on the pilot side upper firewall. Due to the length of my pre-fabricated wire bundles I had to relocate that bundle to the passenger side. Additionally, the neck on the passthrough looked like was going to interfere with the scat tube going from the engine baffle to the oil cooler. Based on that, I had previously removed that passthrough, leaving a 1" hole in the firewall at that location. I hate to patch stuff on a brand new airplane, but that's the simplest solution here. I went up to my local metal supermarket and picked up a scrap of .020 stainless scrap that they had left over from a bigger job for a few bucks. Using the passthrough flange as a template, I fabricated a circular patch for the front side of the firewall and then attached it with a new bead of RTV. On the back side I reused the doubler that came in the passthrough kit and screwed it all together with #8 screws and fiber lock nuts. The lower screw also serves as the ground point for the microswitch that triggers my "Parking Brake On" CAS message. This is a semi-permanent fix. In this configuration, it meets the FAR23 definition requirement for a firewall, but it's screwed together rather than riveted so it's removable without having to drill anything out if I need to send anything else through that location in the future.