It's not feasible to bring it to the airport. Two thoughts: have your friend take a taxi, the T or bus to a mutually agreed upon spot along the Rt. 128/95 corridor. You will avoid the city completely that way. Or, drop the trailer off somewhere near the Rt. 93/128/95 interchange, go into the city to get him/her, and then pick up the trailer and continue south. There are also "park and ride" facilities where you might be able to wait. Your friend can take the shuttle that goes there. The one in Framingham puts you in a good location to pick up I90.