Guage multiplication?

Hi all. I've tried Googling this, but cannot find a clear answer. I know you can run various sizes of wire within a circuit. For example, one would run 0 or 2 guage wire when relocating a battery to the trunk due to distance and power loss, etc. But, then the rest of the wires are 4 guage and higher.

I also know that "The Big 3" upgrade is effectively adding another wire to increase the efficiency and/or power running between those three places. My question is, is it possible/reasonably safe to use that concept when relocating the battery?

Basically, 2/0 guage wire is expensive. Higher guage wire is less so. Could I conceivable run, say two 4 guage wires and have it equal a 2 guage wire? Thank you in advance.