are MHT and boston (BOS) co-terminals? i have no idea what/where MHT is, so i have no idea. despite people in this forum saying that you can't standby to co-terminals, i've never really had a problem unless the fare rules specifically forbid it. and, i've never been on a CO flight in which co-terminals have been forbidden. (NW sometimes sells cheap fares to JFK that don't allow standby to LGA (LaGuardia) or EWR (newark). but, i've never seen CO forbid certain airports from standby.)

if they are co-terminals, you should be able to do it. but, at the end of the day, it is completely up to the gate agent. if you catch her/him in a happy mood, you could be good to go.