If I understand you correctly you are going to take flights on BA in December 2015 and you want to have these flights credited to your account after your membership year resets in February 2016.

If that's the question then I'm afraid the answer will be a resounding 'no'. The tier points and Avios will be credited to your current membership and the tier points will reset to zero (as well as your number of eligible flights) when your membership year renews.

Or have I misunderstood?