Could you not put the bike in the trunk of a Camry if you remove the front wheel? If you have a front fender, it won't work, but might, otherwise. I would miss my trunk mount rack if I didn't have it available. There should be some way of getting a bike hauled on a car—that's what cars are there for! :)

North Station provides easy access to the Charles River bike paths (via Nashua Street). You can ride out to Waltham and back, much of it on either side of the river, and it's quite a nice ride (pavement is better on the Boston side than the Cambridge side, downriver from Arsenal bridge). If you did want to run your bike through Charles, it shouldn't be any problem. The station was redone in the last few years, and there are ascension rooms from street level to the platforms. You just have to be concerned about the rush hour times that the T doesn't want you to bring a bike into their carriages.