Hi. It is an interesting question. Can you confirm (or comment) scenario below?
1) Customer called from his ext -> queue A -> Courtesy callback for queue A.
2) Customer called from same ext and came to another queue -> queue B -> Call was answered.
3) Now you want to remove call from queue A based on customers ext.
This may be a simplistic answer, but if you're thinking you're going to have some other web service or source of the numbers you don't want to call back, couldn't you just do a lookup of those numbers right before you hit the Do Callback node in the CallbackWait script (or even after GetStatus)?
So if you get a match (you don't want to do the callback on phone number 555-555-5555), you return the call to UCCE and release the call and maybe set a special call type to offset this one that was spiked?
In ICM you have Cancel Queuing node.
So that's right, you can check in your custom CVP application if the call with the same ANI was already answered in last let's say 10 minutes and do not make a callback.