I've heard people use very fine wire wool to polish frets before,never used it myself,but mask off your pickups or they will be covered in tiny bits of wire wool.
I polished my frets with Solvol Autosol metal polish about a year ago,coincidently,I'm cleaning my fretboard tonight with lemon oil and the lemon oil is removing the tarnish leaving the frets shiny again.
I protected the fretboard with masking tape when I used the Autosol.