I have been using this method for awhile if you care to try it.
I use either a dremel, drill, or press.
Go to any local shop that carries dremel type bits. Find the one that is a round ball on the end of the shaft. That ball is either a rasp of different coarsenesses, or even better, a sanding ball. The sanding ball is best but the rasp, if fine enough, works quicker with less plugging.
If you get the sanding ball, then also get yourself a gum rubber erasing stick. They are used to clean sanding discs and belt sanders. Using the eraser gives you 5-10 times the life out of any sanding surface. Been using one for 20yrs. and wouldn't be without it.
Rick