Hi Peter, have used this method many times, you need a boat with a flush rear deck, put the bait and sinker on the rear deck then with your reel bail arm open gently move into the position to drop the bait. Depending on the water depth allow for the line drop buy moving further than you need, close the bail arm and gently pull the tackle off the deck. Allow it to sink before moving the boat and move ahead to clear the line.
I have used this method at 100m range, but it is difficult to guess the right spot
Mark