I was thinking about doing this last year but decided not to go that out if state route. But if you have a dealer that is willing and friendly enough you can purchase the car and get the bill of sale (don't have the car registered/titled in the purchase state) that will have the VIN (needed to get auto insurance) and proof that you own the car. One you have insurance you can go to the RMV and regisure the car and get your plates.

Something to keep in mind is if the state that you are buying from does not do temp plates you definitely don't what the car registered out of state because they will want to collect taxes, then when you want to register it in MA they are also going to want to tax you since it was purchased within 6 months (pretty sure it's 6 months)