In SF The Rush was first come-first serve two hours before the show. There was never an issue with getting rush seats, even though the supply was limited. Even on Closing night the rush seats did not fill up, although the show was sold out.
Maybe it will be different in Boston. BTW- The cast is super-nice, if you talk to them tell them their SF Friends say hi!
Some people come into our lives and quietly go, others stay a while, and leave footprints on our heart, and we are never the same.