Too bad the builder was in a hurry and/or didnt care! You have probably seen the rubber grommets that can be split with a knife and installed around a bundle. However, if the wire bundle fills the hole, there is no room for a gromet. Short of removing the wires and doing it properly, the only temporary solution is to use a piece of thin metal wrapped around the bundle and slid thru the hole. Secure the metal wrap with cable ties or tape...looks like crap and is hokey but it just might keep the wires from being cut until you can remove the wiring and do it correctly.

If you have access to a machine shop, you can fabricate a split collar that is smooth in the wire contact area. The collar would be four pieces and two would install from each side to isolate the wires from the raw fiberglass edge. The four pieces would have holes to go thru the firewall and bolt the assembly together.

mike in tucson