Australian hired as Captain on US Flagged boat
For a private US flagged yacht, I believe the restriction only applies while the yacht is in US waters (something about senior crew have to be US citizens or green-card holders).
You could set up a rotation system so that you were only in charge while outside US waters?
There is a category of yachts (private only - no charter, while in US waters) that are "documented but uninspected" that does not seem to require US crew (go to chapter 26 and look at the end of table 26-1). There also seems to be a 200 ton "limit" on some regulations.
P.S. If you are not married there is another solution. Fall in love with a US national, get married and get "imported" - only takes 18 to 24 months (but then you have other problems )