Hi William,
I have no experience with such request, so my idea can be wrong completely: You can try to monitor input queue to check if X button generates any request sent to the queue (I guess it should, but not sure). In monitoring function you can reject this event, do what you need and to send the same event from your application.
It seems there is no documentation how monitoring function should be defined, but Jon provided this information in this older post.
With regards,
Jan