If you're very careful you can use a wood file, then some sandpaper (on a block) to remove the wood yourself.
I did this on my 1999 RG520 that not only had too much wood, but shims as well!!! (I think I measured the nut at about 1.3 mm at the first fret.)
The neck, when I got it, was dead straight and at first I didn't really notice how high the nut was, then I did a top to bottom set up and DAMN! LOL
You have to maintain equal pressure on both sides of the file, and you should use a fairly fine file and do it just a little at a time, checking often how low you've gone (you can use the edge of the fretboard as a reference point).
DO NOT do what I did. I used a fairly course routing file and took off about .5 mm too much (actually woked out okay, once I ordered shims from Rich)
Ideally you'll want to wood to either be perfect, or slightly lower than needed (that way you have room to go up AND down as the guitar ages and the wood changes).
Oh, one last thing, if you do try it yourself, masking tape is a must. (Thank God for paint "marker" sticks. LOL)