Actually, on all my unglossed fretboards, I rub linseed oil into the wood - keeps it at a nice moisture level, and keeps the wood looking slightly darker than that awful "powdery" hue you get with new or freshly sanded boards.
On fretted boards I use a cotton bud soaked with the oil and rub it in so I can get right up to the fret edges. I leave it overnight, then gently buff the board with a lint-free cloth - does the job every time!!!
I have done this on ALL my rosewood and ebony fingerboards over the years - Alembics, Sei Basses (8 of them so far!!), Fenders, Nordy, Lakland and so on.
As for the superglue idea on fretless - you would need an awful lot of the stuff to fill the pores and grain of the wood, then you'd need to re-shoot the neck to get the profile flat - which may result in rub through of the superglue. Also, I am not sure about how the superglue would sustain prolonged playing - might be rather brittle? If you were thinking of a coated fingerboard, you would be best checking out the Thor Epoxy coating site. Myself, I prefer the natural growl you get from strings on wood!! Here's my latest fretless in construction - shouldn't be too long before it's ready now!! (macassar ebony full facings and fingerboard!)
