ohh brain storm what about this crazy concept what if you spot welded the nut on not alot just enough to keep it on and be able to grind it off if you need to take the nut off
ok heres another brain storm now lets suppose you figured out a way to keep the nut on the bolt when engine is running faster than the drill used to start it , you then find sealed bearings to fit snugly with your socket attatch the socket and bearing in the mag cover and make it water tight drill a hole to fit them in seal it watertight and put it on the motor you would then have a simple drill start motor thats water tight the socket would be sticking out a little spinning but since a socket is smooth and cant snag anything it wont hurt any thing
I was thinking about doing exactly this. Have you done it successfully, or know of anyone who has?
Also, I think you could get away with not welding the nut by using the two-nuts method, only with the outer nut being smaller than the inner nut. I imagine one or both nuts would have to be thin, though it probably wouldn't matter for the outer nut. A bit of thread lock couldn't hurt either.
An even easier option would be to just use a rubber plug over the hole and make sure your socket stays on your drill. Remove for starting, then plug it back in. It just seems wayyyy simpler to carry a drill around than to add all the crap you need for electric start (including extending your pedals, which is my big gripe)