Before committing to buying a post test the routing.
Take a nice thin gear cable outer, I also found vacuum lines from a car worked really well but longevity might be iffy.
Strip the plastic off the last few inches of gear cable, this will allow easy entry in the boss and get the bend. A coat hanger with a hook may help to make sure the cable goes the right direction.
Push the outer through from the outside, some grease will help. Cut stripped part off.
Thread the inner cable through. It may be hard to get past the bend at the boss, if so pull the outer through a bit further and it should pull the inner through.
Check the cable runs smoothly. Order dropper.