If it's legal in Mass, why couldn't you get married in Mass and have a "vow renewal" in Disney through DFTW? I think the only requirement for a vow renewal is that you bring a copy of your marriage license. Alot of catholic couples get married in the church first, so the church recognizes their wedding, and then they have a 'vow renewal' at Disney.
http://psc.disney.go.com/guestservices/9053.html
"Q: Are any documents required for a vow renewal?
A: Yes. We must have a copy of your original wedding certificate in order to perform a vow renewal. Sorry, but there are no exceptions."
If you didn't want to do that you absolutely could either plan a magical gathering, with a dinner in a restaurant, or go through event services and plan a dinner/reception/party in a banquet hall, or other location. You can also book things like wishes cruise and illuminations dinner/dessert party, you can book characters, floral, dj etc. About the only things totally unique to DFTW are the Wedding Pavillion, having a wedding coordinator and the in park, in your wedding clothes photo session. You should be able to book all of the same locations and events that DFTW does through Magical Gatherings or event services.
If you chose just to arrange your own dinner at a restaurant, I think you can still order wedding cakes from the GF bakery. In general you can order cakes from any of the bakeries on property (Contemporary has one as well, Mary is one of the bakers there and is AWESOME!)
Good luck, and let us know what you decide!
--Heather