The TCX flights have been quite difficult to decipher given the seasonal changes between the GLA peak period, then shifting the aircraft to STN and so on.
What I can gather so far:
5 long haul aircraft required on Monday's, Friday's and Sunday's.
There seems to be 2 gaps that a MAN-BOS flight could run, which is Tuesday and Saturday, and depending how the LGW long haul flights rotate (ei a MAN based machine or the 5th 'floating' aircraft that goes to STN/GLA), there could possibly be room for a Thursday flight too.
This is of course, based purely on long haul flying and the aircraft could well do a short haul mission instead, which I have not looked into. I know the A330 has been used on MAN-DLM this winter so could well do something similar in 2015.
However, it is encouraging that there are at least 2 gaps where Boston 'could' be run.