Hibernate version: 2.1.8

I have a POJO (plain old java object) that comes from a 3rd party SDK that I would like to persist using hibernate. I have created a hibernate mapping file for it and I am able to save it to the database without a problem.

Now I am finding that I would like to introduce a few fields such as a hibernated generated id (currently I am using assigned keys due to the 3rd party SDK populating the object with a unique ID) as well as createdOnDate and modifiedOnDate but since I can not change the underlying class (managed by a 3rd party) I am not sure what my options are beyond subclassing the 3rd party class and adding the fields then creating a mapping for that object. I would rather not do this as I would have to subclass quite a few classes.

Does hibernate support injecting dynamic fields such as ID that don't exist on the underling class? My guess is if it does it would be quite hackish but if someone has a solution it would be appreciated.

I don't see a way around subclassing, but you could use some tools or scripts to automate this for you.
How many classes are you talking about? Unless its hundreds, you just need to add 6 methods in your subclasses.