Firewall Grommet for Existing Wiring

[JadeMonkeyStang]

When an alarm system was installed on my GN in the distant past, the tech simply pulled out the grommet that runs wiring from the engine bay to the driver's side interior of the car (on the firewall under the brake booster) and ran his wires through the hole where the grommet had been installed. This means that I now have an open hole between the engine bay and the interior. Does anyone have a recommended grommet brand or style that I can use to seal this hole and include both the factory and the aftermarket wiring? Pulling the wires out to feed them through the factory grommet isn't really an option at this point. I know I could cut the factory grommet, feed the aftermarket wires through, and then use some type of sealant (most likely silicone) to make it watertight but I'm hoping there's a more elegant solution.