Yep, get a trailer, put a small portable petrol generator in it and use the generator to drive the ACG starter.
Or replace the outboard motor with one of these babies:
Four decades on two wheels has taught me nothing, all advice given is guaranteed to be wrong
You should add a snorkel to the intake, and you could have an aquatic PCX.
I bet adding an outboard like that adds way more HP for your buck than any other mod too.
If I want more horsepower, I'll probably just put a V-TEC sticker on my PCX. I heard the sticker adds 5 horsepower, or so my friends that drive ricers say.