I've only used stainless steel frets, but have had good success using:
- Leveling file
- Fret rocker
- Fret crowning file
- A lot of different grits of sandpaper 300, 400, 500, 600, 700, 800, 1000
- A sharpie
to do what you want.
Use the rocker to find high spots. Mark 'em with your sharpie to make sure you're hitting the right spot. Then use the leveling file to take them down. Go very, very lightly while doing this or you'll get gouges that are a ***** to remove. Then black the tops of all the frets with sharpie and use your crowning file to reduce the sharpie mark down to a thin line. Then it's just a matter of sanding, sanding, sanding to smooth the frets out. I'd actually recommend buying a dremel with a buffing attachment for this - will probably do that on my next refret.