modding a bell'o sp224

I am wondering if anyone has done anything to improve these speaker stands. This was my wife's choice of stand. But it seems a little lightweight. It doesn't appear to have a provision for filling. The center "swoop" is hollow but there is no cap to keep stuff in. I could pour something in that would harden to add mass and stop any sympathetic vibrations. But I don't have any idea what that something would be. I have also thought that making a black bag and filling it with shot and laying it on the base might help. The two curved pieces that make up the base seem to be pretty solid and have decent mass. Any ideas would be appreciated.