That's a Hibernate Tools (hbm2java) question. If you could do it, you'd have to create a custom reverse engineering strategy or modify seam-gen.reveng.xml for your project.
I looked at the Hibernate Tools documentation and didn't see anything that does what you want.
In any case, post your question here: https://forum.hibernate.org/viewforum.php?f=6
Max Andersen is your guy...
btw, why do you want to do this?
I have now placed the message in that forum.
The why is because I am using GraniteDS with SEAM Framework, I have a large mysql database (well large is a point of view) which I want to generate the code for. However, I have one inheritance relationship in my entities, one super-class. When I run the server, something related to graniteds is not happy and can't see the relationships on these entities unless they are placed at the member variable level !
I don't want to manually copy all of these to the member variable level.