How to delete listener with anonymous function?

Question

I am using MindFusion library for Diagramming. For example, I have that listener:

diagram.addEventListener(Events.nodeCreating, function (sender, args) {

    diagram.removeEventListener(Events.nodeCreating, ????)

});

How can i remove it when my function is anonymous? It works when i will name it:

diagram.addEventListener(Events.nodeCreating, function tmp(sender, args) {

    diagram.removeEventListener(Events.nodeCreating, tmp)

});

but is there anyway to do it without forcing the name to that function? What should i put into "handler" parametr?