If you're handy and have the time and inclination you could build something like these (sand filled "seismic sink" isolation shelves). I don't have any schematics or details, but you should be able to figure it out from the pictures - I did.
http://cgim.audiogon.com/i/vs/i/f/1155818474.jpg
Enjoy,
Bob
http://cgim.audiogon.com/i/vs/i/f/1155818474.jpg
Enjoy,
Bob