Larry,
After some looking into this the AGOL viewer is able to do this because is guaranteed to have the directions widget enabled and thus can have this link to open the directions widget and add the selected feature to the directions widget. The directions widget can take a Point, lat and lon, or a string address. To make this work with WAB you would have to ensure that the directions widget was added to the app and then call the widgets "this._dijitDirections.addStop(theselectedFeaturesPoint);". So to answer your question no I have not tried to add this functionality into WAB and no it should not just work because it does in the AGOL map viewer.
