The problem is this:
There are not standard events sent via AMI regarding extra variables.. parsing CDR events via manager is overkill for that feature. In FOP(1) there is the option to save every channel variable that is "Set" and then pass that to the panel itself, but it is quite expensive on CPU as it has to inspect every event looking for the "set" application, etc.
The next release will have a command "setvar" that can be sent to the client, and that will pass the key/value pair to the notification scripts. But you will have to custom code the event processing in FOP2Callbacks.pm and return a setvar event accordingly. It will consume quite a lot of cpu, but should be possible to do (on a custom basis, and programming it specifically).
The callerid name is handy for passing simple values like this one, many people do not like the idea but sometimes it makes perfect sense, it does not consume CPU and it is easy to implement without disrupting anything.