If Starnan knows his HRE mechanics there is a way to completely dismantle-proof the empire with 2 button clicks.
Hint: you cannot declare on a prince while at war with the emperor.
I was going to write this, but assumed it must have changed for Kaiser to say that. But in truth, this mechanic pisses me off. I can get not declaring on a prince while allied with the Emperor and in a war with them as such, but not when you are at war with the Emperor. Is it because you can't be at the same war with the same country twice and the Emperor is autocalled?