If I understood you correctly, you want all your classes that derive from one base class to be saved in one database table? If that is the case than you need to use "flat inheritance". For more information you can refer to the article How to: Model Flat Inheritance with the Visual Designer
Please find attached a sample project I have prepared for your convenience.
Do not hesitate to get back to us if the project is not the proper solution for your scenario.
the Telerik team
Q3'12 SP1 of OpenAccess ORM packs Multi-Table Entities mapping support. Check it out.