Jeff,
I flyfish Martha's Vineyard each summer and have found excellent stripers off of "Dogfish Bar". Go down to Menemsha and ask around where you can find this spot. Also, when on the Vineyard it would benefit you to ask around and see if you can locate Cooper Gilkes (try Dick's Tackle Shop in Edgartown) or ask around for Chris Reardon (a friend of mine) both are excellent folks and more than willing to lend a hand to enthusiasts. As for flies, you would be well served with a good old-fashioned deceiver, as well as some Surf Candies or Sand Eel imitations if you plan to fish the shore at all. Good Luck and happy fishing!