addRelation between referenceplane and 3dsketchplane

Hey,

i try to add a COINCIDENT Relation to a 3dsketchplane to a referenceplane of the assembly. How can i add this relation? I didnt found a way to convert a selected Referenceplane to an entity ( Sketch.addrelation (entity, relationtype)   )

Do you know how to add sutch a relation?

SolidworksApi macros