I understand your frustration- there's a point where we all throw in the towel. I'm including this in case it helps and you might want to give it one more try....
It is a tight fit through that area and is going to be much harder, if not nearly impossible, if you route it from front to back - unavoidable in your situation. This photo shows where my aux lighting cable routed through next to other wires. I would suggest, if you want to give it one more go, to run a stiff wire through from this side to the front of the tank.
Very securely tape your connecting wires to that wire and pull them back through that opening. Lifting the tank a little (don't force it and stress the fuel line connection) may allow you to help them along through that bottleneck. If you can pull one wire at a time, even better.
You can also do your own 600 mile service if you document it. You can find other people on here who have also done that. I've now done the 10 and 20K (with valve adjustment), as well. Not everyone wants to do that- understood. I'm pulling for you, however, on running those wires if you choose to do so.....