>Another possibility is to pass a reference to the calling object as input to the class at creation time; have the form populate a member of the passed object, creating it as necessary.

Why? Why not either just pass the parameter/return object every time, or just pass the parameters and expect a return value in a specific property of the called class. I don't see where using the calling object as the parameter object would be an advantage. If they're developed seperatly, the called object could stomp on useful properties in the calling object.