Wouldn't want to break that trend of your incredibly helpful chime ins 😉
In regards to OPs question, one solution is to cut the metal seal that surrounds the outer door. This gives you a pretty good channel for wiring without overly disrupting the internal layout. I did this back when I ran an extra power supply for two gpus in my 4,1 but your case may differ somewhat.
Wasn't pointing on using the proper cable instead of "this" helpful? 😉
6 to 8-pin cables are widely available and cheap.
Why to do something wrong when you can do it right?