Yeah, Wellington works great; or you could do Sullivan Square, right off the Sullivan Sq exit off I-93 in Charlestown. Wellington and Sullivan are both on the Orange Line. Fare is $2.00 each way if you buy a "Charlie Ticket" (paper), or $1.70 each way if you can get a "Charlie Card" (plastic). Ask a T customer service rep for the plastic card.
You could also park at the Cambridgeside Galleria, and take the Green Line from Lechmere. Or even walk; it's not too far. Or park at Anderson/Woburn (has its own exit of 93) and take the commuter rail.