I have one of those "wiper blades" used by window cleaners, which fits over the end of the disassembled inner (hooked) part of a standard two-piece alloy boathook. Used from the dinghy it gets to most bits affected by the light.
Having said that because I launched late this year, and have sailed every weekend but one since, there is only a slimy line along the waterline and irregular patches of slime elsewhere, so I haven't used it yet this year!
It used to produce reasonable results on the previous boat.
275/30 "Cascada"