Declaring war without a CB is an option, provided your AE is low enough. Also, are you sure that every neighbor is allied to Spain? You can fabricate across a single sea tile. I believe you had a port on the Adriatic, so you should be able to fabricate in the Venice-Croatia area. Likewise, you should be able to fabricate across the Ligurian Sea all the way to Provence. Also, are you sure Spain is an ally, and not the defender of faith?
Failing that, you could use the "join war" tactic. Basically, you wait until a neighbor is in a war, then separate peace out. You can do this by using the enforce peace interaction, in which you will need +100 opinion with the defender, the attacker must have -25 war score or higher, and you can't have a truce with the attacker. (The last point would be moot in your case.) Also, you can directly ally the enemy, then break the alliance after the war (or not). When doing the "join war" tactic, you will need to peace out before the war leaders do. Watch the war enthusiasm, and try to take as much land as you can as fast as possible. Battles don't affect the warscore of allies. If you single-handedly win the war, but give all the provinces to other nations, you have 0% war score to negotiate with.
