I've used paste wax, mineral oil and mineral spirits with the pumice powder to rub out a shellac finish. The paste wax produced the best results in my personal opinion. It was applied using a lint free cotton rag bunched up like a french polish pad and rubbed in a circular pattern and later changing direct to go with the grain of the wood.
I've also had good luck using pink stropping compound shaving when I didn't have pumice available. It really refines your finish and looks amazing.. its not quick though so pull up a chair and put on some good music in the background.
This is what it looks like after a fair bit of elbow grease.. quilted maple and solid ebony inlay.
I've never used it as a grain filler before.