Daggerboard Groove

Im looking to setup some daggerboard raising lines, however, there is no groove in my daggerboard slots or on the daggerboards them selves to allow room for the line to go down the slot with the board. Id rather put a groove on the daggerboards than on the slots in the hulls. Whats the best/easiest way to cut out a groove in the Daggerboard to allow the line to go down either side of the board and through the hole through the board.
They are the older style 12inch fibreglass round bottom boards with no handle or cut out area near the top of the boards.

Cheers,
Michael.

One thing I would say is you don't have to go down both sides of the board. You only need a slot on the inboard side. There's no need for 2:1 purchase to get the boards up.

I guess use a router and then glass it back up to seal it - assuming there's foam inside. You may want to make the slot a lot wider than the rope though to help avoid it jamming in the slot.
On teh other hand I guess you could also cut out a complete hole right through - use one of those 50mm holesaws at the top and bottom. That could work - and no fear of the rope jamming then.