Fit file encoding

Hi, 

I'm currently encoding Fit files that represent a workout routine i.e., a Workout File as described in section 8 of the document "FIT File Types Description". What is not clear to me is if there is some way to insert some custom metadata in the file so that to be retrieved in the resulting fit file that represents a workout result i.e., an Activity File type.

I need a way to link that a certain workout result is associated with a certain workout routine to basically link the "planned part" of a workout to the actual performance of a user.

Does anyone know if Garmin watches/platform propagate some metadata from a Workout File to the "associated" Activity File?

Thanks