I did that on my Gen1 E19. I've fished a lot of wires and that was one of the trickier ones. Part of the problem is ETI's habit of rather freestyle wiring.
There's lot's of wires and they're not all that well bound together in a loom.
There's a chance of getting entangled in an errant wire along this path.
I used a flexible wood batten. I only intended to snake through that path once. You can see the white cord. It's over twice the length required and stays in place. This allowed me to later pull several other wires through.
I did get snagged a couple of times but it's one of those things that might take a little bit of patience. Easy for me say now but at the time there was a little muttering and cursing.
By comparison the path in the 21C is really easy.
Ron