How many objects do you need to create this way? Maybe it will not be such a bad idea to add a bunch of events like this:
If enemyType="Zombie" Create EnemyZombie
Combine all such objects into a family, define an instance variable LevelBuilderCode and use it to link your C2 object with your level builder object. You'll be able to select any object/instance by picking family member where LevelBuilderCode="..."
As for the object-specific instance variables, maybe consider replacing them with dictionaries. You can attach an instance of a dictionary to each object and this will give you an unlimited number of variables which you can easily add/remove/modify in runtime.
One more thing - to minimize the number of objects, group similar objects in one sprite with different animations. Animation name can be passed as a string from your level editor.