Maybe making a proxy like so:
class A loaded by a classloader C1 denoted <A,C1>;
another impl of class A loaded on a second instance of a classloader C2 denoted <A,C2>;

whenever we want two classes loaded by diferent classloaders to communicate the jvm allows that by way of automatically creating proxies. In the case where an instance of class B loaded by C1 denoted <B, C1> want's to communicate with <A, C2> the JVM creates a proxy <A2, C1> that resides in the C1 classloader.

I dunno, maybe it's easy said than done?

regards,
johan