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.
You can improve the situation somewhat but you’re never going to get a prebuilt like that as clean as you see other people’s diy builds with parts chosen taking aesthetics into account.