Dynamic proxy with custom methods

I am trying to write a generic wrapper for javax.sql.DataSource instance. My problem is that this class is configured by calling setters on the implementation - in configuration I get some properties with foo=bar and then setFoo("bar") is called on the data source. These setters are not invoked using interface calls but using reflection.

Now, when I want to wrap an implementation, I cannot know until runtime what setters it has. I would need a java.lang.reflect.Proxy that would, in its getClass().getMethods() return my own set of methods, not just those that are defined in the interfaces.

One way I can see is use Javassist and generate a custom interface whose methods would match setters on the instance of DataSource I got, and then provide this interface to the proxy factory method. Is there any pure Java rt.jar way to achieve the above, without additional dependencies (to Javassist or CGLib or ...)?