Am not sure about if it can be done in the version you are using, but ...

Create an interface and put it on your content types that inherit from your base class. Create a UIDescriptor for the interface.

[UIDescriptorRegistration]
    public class IPageFooterlUIDescriptor : UIDescriptor<IPageFooter>
    {
        public IPageFooterlUIDescriptor()
            : base()
        {
            this.DefaultView = CmsViewNames.OnPageEditView;

        }
    }

After you have done that you can use the interface in the AllowedTypes attribute.