You could unscrew the EVA/plastic deck plate and remove the center board and it's locking mechanism.
Then cut some closed cel foam to make filler piece (or leave it void would work also).
Then make up a new solid top plate from materials similar to the original deck plate (use the original deck plate as a template) and cover/seal the top of the centerboard slot.
You might remove about 5-7 lbs. (2.2-3.2 Kg.) but you probablly won't improve the performance of the board as much as you think.
It will not affect the balance of the board, but purchasing a GO or Carve/Futura is a much better way to get the performance you are looking for.
Hope this helps,