I've threaded the needle with that cable on my two 400's six or eight times. Sometimes it takes a few tries, but it always goes through without too much drama. I'd make sure the end is soldered and has a bit of a point to it and then fiddle with the bends. I'm sure you can get it to go. Patience grasshopper.
Gratuitous shot of the one I most recently rebuilt. This is an amazingly nice bike to ride:
- Mark