Steve's correct. Putting holes in the forward seat locations will allow water 
to enter the cabin through the passageways under the seats. A close 
inspection will show you what we mean. If you do want to install drains, it would 
require the installation of a hose that would take the water down to the cockpit 
floor. I haven't found a flush mount that would do the job properly.
As for the centerboard drain hole, pulling the line up slightly and locking 
the ball into the cleats will open it up some. If the drain is clogged, simply 
pulling the line up and down a few times should clear it.

Rummy