Canceling a JSONP callback?

Hello all,
I'm wondering if anyone here knows of a reliable way of canceling a
$.getJSON request for cross-domain JSONP.
For example, is there any way to figure out the name of the function
that jQuery appends to the window (such as "jsonp1222912605851"), so
that I can just replace it with function(){}, and prevent the original
callback from executing?
Any help appreciated,
Jed Schmidt