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?