How to add a new slide and replace an existing slide on the fly with jQuery cycle?

I'm using jQuery cycle plugin right now, and I want to add a new slide based on the newly created image and I want to replace this slide later if the user has updated the image. I read the document of jQuery cycle, and I found it's using onBefore callback to do the job, but it's not on the fly, how could I do it on the fly? Thanks a lot.