@Drox yes, i think it could work - just try it out with a standard 5-pin MIDI cable, i think nothing too bad can happen 🙂.
If it does not work, you could try to modify the MIDI cable so that only the three bottom pins (2, 4, 5 on the OUT pin in the schematic above) are connected. But building the splitter is recommended - it’s the “cleaner” method with only the relevant MIDI data on their respective pins - and you gain an additional IN port 🙂.
Best regards and enjoy!
Peter