[dungeonguru]

Look at the community Barbarian Path of the Totem Warrrior.

You'll see that the configurable is pretty simple and the scripts that affect it are run inside the class Custom Ability.

You'll also see where the script inside the subclass is referencing xTotalLev to get the total class levels.

You can do something similar outside of classes (like if it's a feat or boon) using the #totalvelcount[] and/or the #levelcount[CLASS_ID] macros or even do a manual count of the Class.? tags.

EDIT: Additional thought.
If you're wanting to use one of the Activation fields on a class special/feat, you can play around with the fields like actUser. This is where you have an Activation and you can set the actUserMin and actUserMax to show the amount of activation if that makes any sense.