The only data points you can add to an instance is the Data / XML fields.  I've seen cases where XML fields have been used where a an XML field was created that leveraged a repeating node in the schema and that XML field was updated via Server Event(s) throughout the process with the custom audit/tracking data.  Then the UI/Forms for the client pages was updated to show this XML field to provide insight into what was being tracked.  Additionally, data can be written out at the desired points in the process to a custom database.

Perhaps it might be helpful if you can provide some more details about what it is you're trying to audit.