Obviously, the best solution is inside the mast but if you don’t have room then maybe look at something flatter to shape to run up mast? If there is a section inside the mast that is separate, have tubing from duct into that area of the mast, and the mast section fills, then install nipple and hose coming out of mast near the board??
We have a design where the impeller nozzle that is 3d printed has the water inlet and area embedded within the 3D part and is accessible near the aluminum tube which is streamlined. But, we are planning on doing CNC aluminum parts with a lightly different design it looks like.