Hey, a thread on dismantling the HRE... and I just did it, like ten minutes ago. What a coincidence.. lol
I didn't plan to dismantle the HRE, but somehow Austria was being a total asshole and got themselves a nice coalition, which made Bohemia the Emperor, and then Savoy. As soon as I saw Savoy was the new Emperor, I decided to go for it. As Tuscany, I had most of Italy except Corsica and the original Venetian provinces.
The rules are a little bit complex, but you DON'T need to siege down every single elector capital. In fact, you only need to be either allied to all electors, or have their capital sieged down. The rules are rather byzantine, so I'l just retell what happened in my game. The electors are, as you can see, Bohemia, Brandenburg, Cologne, Mainz, Palatinate, Saxony and Trier.
* Palatinate, Cologne and Trier were allied to Savoy. I allied Bohemia, Brandenburg, Saxony and Mainz. Even before DoW'ing Savoy, the allied electors were "not independent."
* Brandenburg DoW'd Bohemia, calling in Austria. This made Brandenburg "independent" since the alliance broke. Austrai sieged Bohemian capital, which made them "independent."
* Seeing the chance, I thought I'd DoW Savoy and bring in the rest of the electors on either side of the war. Palatinate, Cologne and Trier were "independent", while my allies Saxony and Mainz were "not independent." I sieged down Piedmont and the emperor-allied elector capitals, they were then "not independent." I vassalized them, again "not independent."
* I didn't siege down Brandenburg, so they were still "independent." Brandenburg peaced out Bohemia and made them annul all treaties with me, and after the war I re-allied Brandenburg. Brandenburg was "not independent", Bohemia was "independent." This left only Bohemia "independent" elector.
* Unable to ally Bohemia back, I just sat on Savoy and waited out the five years. Damn you Brandenburg.
* During the time, the Palatinate had a peasant revolt and the rebels sieged down their capital. This made the Palatinate "independent." I had to go save their ass.
* After sitting on Savoyard capital for five years, I allied Bohemia again. After this, I was able to click "HRR auflösen"... "Dismantle HRE" button.
So, it certainly is easier when there is a weak emperor (like Savoy in my case) but it is not necessary to get into war with every single elector at once. As I dismantled the HRE, Brandenburg and Bohemia were not even at war, but just being allied to me was sufficient.