Bus from a park, although you could get the bus to DHS which isn't very far anyway and walk about 20 mins or take the boat from there to the Boardwalk, by the time you've boarded and been transported on the boat you could have walked it anyway.
only go to Studios - Disney Hollywood Studios - at Epcot you have to enter Epcot to get to BW. so you are using up one of your passes (unless you have park hoppers)
if DHS has been closed for an hour or more then to get back either take a bus to DD or to the park which has EMH evening - if it is still open.