Perhaps revoking a reform could work like Concede Defeat for something like 50-60% warscore (and the AI adjusted to understand that that is something you want to take rather than a random core revocation and some money)? That way, you could erode the emperor's power without needing to siege down all of Austria (and fighting off all their allies.
Another possibility would be a Revoke Reform CB, which would lower the cost of revoking reforms by a lot but give massive AE for everything else except money/treaty cancellations.
Another possibility would be a Revoke Reform CB, which would lower the cost of revoking reforms by a lot but give massive AE for everything else except money/treaty cancellations.