Some sort of product that works in an aerosol spray can would have definitely made the process easier.
I simply had a 1L bottle of the stuff (boiled linseed oil) and a syringe the local chemist was nice enough to give to me for free.
What started out as a methodical, clean, well-thought out approach on the bike stand in the garage, soon deteriorated into me eventually pouring the goopy mess into the frame with it dripping and flying everywhere as I stood out on the street in the gutter.
I'm pretty sure I did a very thorough job, but wow... that turned out to be more of a job than I expected.
Still drying the frame right now, alternating hanging positions/orientations to make sure it all drips out and it dries evenly.
Fish oil, eh? I wonder how that smell compared with linseed's oil smell (which wasn't terrible, but definitely noticeable).