Lab-type rubber bottle stops or asthma inhalers have proved useful in earlier cases.
The true NG-style nerd solution, however, is attaching a much more beefy L-bracket to the existing one. I did a similar modification to the wimpy tripod foot of my 500/4P, like the attached picture shows. Due to the need for rotating the camera, even this solution cannot be perfect, but should surely help a lot. It did wonders with the 500/4.