Katomi,
Adding mass to a system lowers the frequency of the motion. However, beware that lowering the frequency may push it right into a resonance of the structure. For a tripod with the column extended the frequency that the column wishes to sway may be quite low.
My job involves laser diagnostics so I've picked up lots of tricks for keeping things steady. One is to constrain the motion of the column by pulling it one way or another. In this case I like to use steel wire to connect the top of the column (just below the ball or other head) and tie it to one of the three feet of the tripod. I have a special set of pliers that twist as you pull to twist the wire together but you can loosely wrap the wire around the shaft of a screwdriver and tighten the screwdriver like a garrote.
Yes, you're intentionally adding stress to the tripod which may not be good in the long run. However, the resulting system will be in tension and wish to vibrate at a much higher frequency (like strings on a violin or guitar). This is good since the energy involved in a vibrational mode goes as the frequency squared (it generally takes a lot more work to swing as far at higher frequencies). Just remember to level and frame your shot after tensioning the system.