Mary,

My idea was to have a pocket in the head of the (squaretop) sail where on either side a sealed piece of plain styro foam can be placed. A 500x150x50 block on either side should be enough to provide 7.5 kg * 6 mtr counter leverage = 45 kgm. That would be the same as a 1.60 mtr tall 50 kg sailor hanging of the righting line.

And when done this way it will not look badly at all and it will be aerodynamic (end plate effect anyone ?) . Another ideas is to stuff the top of the mast and the sleeve of the mainsail with shaped (and sealed) styrofoam.

As styrofoam is commonly available for a few bucks you can just replace it now and then.

Wouter