I don't imagine it would be easy to find something that specific (unless someone happens to have found a similar replacement). Especially finding something that implements the same/similar callbacks and options would be hard. No matter what you end up using though, it's likely that you'll need to do some rewriting of code.
This doesn't necessarily have to be a bad thing though, it might be a good opportunity to try to find an editor that works better. If it doesn't exactly fit in to the current system, small changes are usually not a big deal to make (but that probably depends on the site and who does the back end dev on it).
I'm sure you've seen list posts that show some inline editors; might be a good idea to try to find an awesome one and mould it and your current system to work together nicely.
(P.S. My condolences for having to convert a Prototype based site to jQuery - I'm pretty sure I've had nightmares about doing something like that)