hi Ellen,
with the new patch from Eric :
https://github.com/mne-tools/mne-python/pull/556
you should be able to do:
events = mne.event.merge_events(events, [1, 2], 3, replace_events=False)
event_id = dict(Auditory1 =1, Auditory2=2, AuditoryAll=3)
epochs = Epochs(...)
mne.fiff.write_evoked('auditory-ave.fif',
[epochs['Auditory1'].average(), epochs['Auditory2].average(),
epochs['AuditoryAll'].average()])
HTH
Alex