Both authors of the paper you mention were students of mine, so I know the paper quite well! The method is called "Apery acceleration" and has been described in several places (if I am allowed some self-advertising, look at Section 7.5 of my joint book with K. Belabas "Numerical algorithms for number theory using Pari/GP", AMS Math surveys and monographs 254). To answer your specific question, we tried very hard in the 1980's to find a CF for the tails of $\eta(3)$ of the form you mention, with no success. I will soon post on the arXiv a much longer explanation of the method.