Autocomplete : not select

Autocomplete : not select

Hi - 

- could some kind soul suggest how I might  invoke an "on-not-select"  callback after a user has typed something into an autocomplete box but NOT found what they are looking for... 

I want to force users to search a database, and if they can't find  an entity, only then offer them a link to create it. "Select" only fires when something is actually selected... 

Any help much appreciated.

Nick May