Just a few thoughts.
The same sort of regs apply to home built aircraft, and many people employed a separate company to 'home build' their plane for them.So the government inspection dept insisted on photo evidence that the registered owner was participating on the actual assembly.
...
Maybe an option; employ some of the boatyard staff to build your boat ' privately' with your on site participation.
I suspect one could do this an be legal up to a point. I do not see anything in the EPA regulations that would prohibit this at all. The closest regulation might be around 50% build requirement. One could certainly get the hull built by a yard and then do the interior. The hull on a metal boat is a small part of the work effort and cost so I don't think the EPA would care. Certainly one could contract out other work on the boat.
The problem with a home built is that one is looking at a good 5-10 years to do a build.
Later,
Dan