Calculated Parents as Top Nodes

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On calculated parent for nodes in Hierarchy, I have a dimension that is a hierarchy but is currently flat with no parents.  Is there a way to set the default parent to be a top node as this dimension is based entirely on a subscription?  Currently we have to delete the subscribing node and re-create each time.  

The flat hierarchy is used as an attribute dimension in Planning.  I'm hoping going forward we can create a parent, but right now its entirely flat.  We have a subscription from a separate dimension and pushing that dimension with a name transformation into this dimension.