Snaking a 4 guage wire is tough and may cause some white hairs to sprout. If you would like to snake it, best place to do so is to run it where the fuse box is located in the engine compartment. You would have to move the fuse box aside to get it thru. But if you want to take the easy way out, drilling is the best solution. I'm assuming the 4 guage wire is to power ur amp. The area you should drill is located where the clutch would be. You will notice where the clutch would be is a outline which is the thinnest part of the firewall. Pick a sizeable drill bit. When drilling, you're going to have to push really hard. Watch out for the bits of metal because they are HOT! Use a filer or sand paper to smooth the edges out because you don't want to damage the 4 guage wire. Finish it off by applying silicone after u have run the wire thru.

Good luck!