One idea might be to write a C++ program to communicate with the ActiveX control
and expose some JNI calls so that your Java client can communicate to the
ActiveX control through these calls.
It would take some siginificant research to determine what calls you want
exposed through the JNI interface.
It's not too difficult to expose native methods to Java. Also, it is very
easy for C++ to communicate with ActiveX controls. JNI might be a good "bridge"
between the two pieces.