You can run multiple wires to share the current. Presuming the supply and ground are the same gauge, you'll need just as many ground wires as supply. A single larger gauge wire may be easier to route and provide more flexibility than a bundle of smaller wires.
If you run all 4 traces in parallel, and each trace is .85 ohms, then your overall resistance is 1/4 that, or .2125 ohms. To keep the resistance at .85 ohms, you'll need to wire it so that pairs are ran in series and then each pair is ran in parallel.
If you're worried about the aesthetics of having all the wires, you can open the supply (unplugged of course) and clip the unneeded wires inside the case. Just wrap them in a bit of electrical tape to make sure they don't accidentally contact the case or each other and they are out of the way.
If you run all 4 traces in parallel, and each trace is .85 ohms, then your overall resistance is 1/4 that, or .2125 ohms. To keep the resistance at .85 ohms, you'll need to wire it so that pairs are ran in series and then each pair is ran in parallel.
If you're worried about the aesthetics of having all the wires, you can open the supply (unplugged of course) and clip the unneeded wires inside the case. Just wrap them in a bit of electrical tape to make sure they don't accidentally contact the case or each other and they are out of the way.