back to back to AMS would work with one leg in CE that would be 40TPs comes initially to mind. Or a one way and then get the train back, Same would apply to Paris and Brussels. But that could get pricey.

That might be cheaper than 2*ET returns plus would be quicker.

There are literally dozens of 'how do I get X TPs' threads so have a scan down the board for those.

And in your case the 8th is a hard deadline. The two week extension period that BA usually allow to earn TPs in the new year to credit to the old year won't apply.