Well, I've slept on it, and I still don't see any satisfying way out of this mess.
Here is the line of thought that has led me to a conclusion:
1) I agree with Toma and most people, that getting your ally's ally into a war with Enforce Peace clearly violates rule 7.
7. A general anti-exploit rule. Basically, if it looks like an exploit, then don't do it.
In this case it also violated the maximum number of human alliance, but that's not
really important since they technically could have gotten Aragon into the war with some alliance ad-hoc jumping (whether this also violates rule 7 should be discussed for next session imo. I think we should have some quarantine between jumping between human alliances next session, as it makes it too easy to effortlessly switch between wars and blocks. If you can do it even mid-war, then what's the point of the rule at all?).
At the same time I agree with KingSnake, I don't want to win, not even a single province, because of a rule technicality and I would feel pitiful if I did.
So: I don't want to continue in a losing game due to an exploit, nor win because being anal about the rules. It would take all the fun out of continuing this game no matter how we solve it.
2) I can't imagine a two-block game with one side consisting of all the human continental European (and Western Tech) Powers being any fun at all. If it's not possible to fight a war with Brandenburg over a single province without Aragon joining from half around the globe (to protect their ally Burgundy's ally from losing a province?), I can't see how PvP wars is viable at all. (PvP wars have other problems too, yesterday it was impossible for us to peace out and claim a single province with +50 warscore. This means in defensive wars you can drag the war out forever, and hope that something will happen sooner or later to your opponent. I think it could be an idea to make it possible to peace out at +50 if you grab only 50% of your score or something?)
3) Because the war went on forever, my country, and even more so Toma's, is a fucking mess.
3) Nothing will ever top yesterday in terms of craziness and fun.
tl;dr: