The pc does not have back compartment, nor anyway to attack the cable to. What I am thinking right now is to hot glue some zip ties to the centre gap between HDD and mb. And then zip ties the cable to the zip tie, so it runs down the centre of the pc cleanly and branches out to its destination like a upside-down tree.
I don’t think there’s much you can do, nor would there be much of a point to it. It doesn’t look like the cables are currently blocking the airflow and you’re not going to get the inside of this case look aesthetically pleasing anyway. Presumably the side panel isn’t glass either, so you’ll basically never see it. Personally I’d just close it up and forget about it.