Peter,
Sand is cheap, it might work. # 9 lead shot is great at $1. a pound from your local sports store, but you need an oil or elastomer to transfer the energy from the tubes to the lead shot.
As you mentioned,the best solution is to remove the table from the listening area. A craftsman would rather hear beeps, boops and booms, and see his creation, where an audiophile only cares about the sound. We all fall somewhere in between.
As Raul says,"Enjoy the music.". I think he needs to coppyright the phrase.
regards, Ken
Ken