Christy on s/v Hello World has done the research, and gives us the results of it:
These past two weeks of (planned) vacation, we've ended up doing too much (unplanned) boat project work. Ugh. But we've gathered a bunch of ideas from some experts on running messenger lines that we thought useful to pass along...here are the big three:
1) Gravity: tie something flexible and heavy to your line at the top of the run and use gravity to do the trick. A bike chain or a line of nuts seems to work pretty well in some applications.
2) Magnet: using (non-stainless) bolts or some other metal tied to your line, get yourself a decently powerful magnet and lead the line where you want it to go from the outside.
3) Vacuum: tape off all other inlets/outlets, use your shop vac to pull a string tied with Kleenex through the run (this worked particularly well on our bow pulpit).
And when you finally get to running your electrical wire, decide on a suitable knot (we use 1-2 rolling hitches) and grab that KY Jelly from the bedroom and put it in your toolbox.