I wouldn't. If your engines are stock, too much oil could actually build up as carbon deposits in the combustion chambers, sometimes called "coking".
THis is because oil burns hotter than the fuel, so if you run it rich on oil, it could "coke" up, and that's not good.
Mercury Marine spent gozillions designing those motors/injectors. While no company or design is perfect, if they don't tell you to add extra oil, don't.
Good luck with your Donzi!