Any thoughts are using Winair through St. Maartin? It apparently have a codeshare with US Airways and can do it in a single day return via Charlotte.
BTW, I have this worked out now where I can fly American down and US Air on the return and end up with no overnight layover for about $900 RT including the flight to DOM.
Since they are soon to be the same airline, this looks to be the way to go for me.
Looks like there are options out of St. Maartin starting about 2:30, so I could use either the contract or the charter to get from Dom to SXM on the 31st.