Select Parcel options - New, Add to, Remove From

I'm trying to implement 3 options for selecting parcels in my workflow: New Selection; Add to Existing Selection; Remove from Existing Selection.  I've been able to implement the first 2, but not the 3rd:

1. New Selection - RunExternalCommand "ClearSelection" + SelectFeatures
2. Add to Existing Selection - SelectFeatures
3. Remove From Existing Selection - ???

I've studied the Selection Commands, FeatureSet Manager Commands, and Markup Commands, but can't figure out how to implement this.  Please help!