You don't say how comfortable or capable you are at rooting around in the concrete5 directory structure but it might be as simple as replacing the jwplayer.js file and the player.swf file in the existing package.

I assume you have a commercial license for jwplayer since you purchased the add-on originally so I can't see any licensing issues.

First of all, is there a link to a page where your current jwplayer sits? Perhaps we can see where it is storing it's files.

Try to find the package under '[root]/packages/some-jwplayer-like-name' and dig under there for a copy of 'jwplayer.js' and 'player.swf'.

Download the most recent version from here:

http://www.longtailvideo.com/players/jw-flv-player/...

Unzip the archive to your local computer and upload only the two files in place of the old files. Don't just over-write the old files because you might need them if the new ones don't work so just rename the existing files to something like 'jwplayer.js.old' and player.swf.old' so you can swap them back if need be.

It's worth a shot if the original developer is unresponsive and your current add-on doesn't work.