Why not leave the cahh at home and take the commuter rail they also have free wifi so you can surf the net or just take a snooze while you ride into Boston, read the paper or whatever.
you could get the Red Line at "South Station"
and then get off at Park St. and catch the "E" train to Longwood or "D" train to Longwood whichever one shows up first.
There's also a masco shuttle bus (for the longwood medical area)
an express bus to Ruggles station (Orange Line) from which you could go a couple stops to Back Bay and get the Needham "T" commuter rail
or vice-versa
http://www.masco.org/transit/Importe...ess%20Maps.xls
MASCO - Medical Academic and Scientific Community Organization, Inc.