Thanks - in hindsight that seems so obvious!
But now I think I have a hard challenge! I would like to remove/hide the part in the edit widget which shows what layers you have editable with a checkbox beside the layer. You can turn on/off the editable layers with this check box. In my case I am using the editable FeatureService just as a dummy layer but am symbolizing the layer with the MapService instead - so now when you uncheck the editable layer in the edit widget the layer is still visible because it gets its symbology from the MapService instead. I did this because I needed the user to not be able to select all the different templates.
Anyway - I have looked for this check box in every skin...including the EditorSkin.mxml directly in the api download....can't find the reference to it..