There are large grommets on both driver and passenger sides of the FW. I have shoved some pretty large wires thru each of them. They are 2 layers thick, so you need something with an edge to get thru both layers, but there is pretty good clearance between the existing wire loom and the outer edge of each grommet. Poke at it with your finger before cutting any holes you'll see what I mean.
I suggest going on the passenger side, there is less in the way under the hood and under the dash. And if you add another battery it is closer.
depending on the size of power wire, i prefer to drill my own hole. use a grommet. its a much cleaner install. plus, when you use a tighter grommet and hole just large enough for it, it really helps support heavy 1/0 wire.