Get graphics layer created in one workflow from another

I made a workflow that creates one or more graphics layers with UpdateGraphicsLayer. The Graphics Layer Id is not hard-coded, but assigned dynamically.

 

 

 

I want to make another workflow that enables you to deleted one or more of these graphics layers. Using RemoveMapService I can remove a graphics layer I made, but only if I know it's Map Service Id. So I was looking around for a way to request a layer list. From this post (https://support.geocortex.com/essentialsGSCForum?sub-nav=forum&main-nav=essentials&#!/feedtype=SINGLE_QUESTION_DETAIL&id=9066000000008vdAAA) I found that this is only possible for layers with custom properties. So I want to add a custom property to my graphics layer after I create them. How can I do this? SetLayerProperty asks for a Map Service Id I don't have.