Have select HRE powers win out over several wars from Westphalia onwards and eventually leave two-four houses that intermarry. Bavaria, Brandenburg, Austria, Saxony, and Hanover are seem like the most likely choices. One might be "induced" to join the rest with junior members forming some sort of "Senate of Noblemen" or "House of (dis) Honor". This leaves a Gross-Deutschland with Austria, Bohemia, Germany, Luxembourg, most of Poland, parts of Denmark, and chunks of Italy along with parts of the Balkans in one state. While the Hungarians and Serbs may seek their fortunes elsewhere, the massive state could be integrated into a powerhouse that could dominate Continental Europe and be a match for any other power. Playing its cards right it might also be able to play a major role in colonizing the New World and building the Americas...or perhaps the Amerikas...and playing havoc with Napolean, the Ottomans, Russia, and perhaps challenging the UK at some point. The seeds of German nationalism are there though who is "German" and who is not is still malleable at that point.