Can I disable Observers from a single controller method?

I need to stop an after_update Observer method from running, but only in one method of a related controller. I want to be able to change the sort order in acts_as_list without triggering the whole after_update business, since nothing that that Observer was interested in has actually happened.

Alternatively, is there a finer-grained way to call the Observer? Something like Prototype.js's synthetic events as defined in