Federalization is a modern concept that requires 18th century constitutional systems, when the HRE was in its death throes.
What you might mean, I surmise, is the best PoDs for a centralized HRE. In such a case, a string of fairly successful, talented, and longeve Ottonian or Hohenstaufen Emperors, with no dynastic crisis, that spans a century or so may do the trick. No premature death of Otto III or Henry VI would be a good start.