Well, that 'future situation' developed rather sooner than I'd have liked. Five 500ml PET bottles of blueberry hydromel were found to be rather swollen. Carefully transfered them to the freezer for half an hour, before slowly opening then inside a carrier bag over the sink. They had been stabilized and in the bottles, showing no signs of any activity, for over a month - not sure what caused them to start up again. I think the lesson here is to keep things under airlock for much longer after backsweetening.
And to top it off, a braggot I had rather high hopes for appears to acquired some sort of infection - lots of white flecks on the surface, and producing gas despite having been fermented dry.