PowerBI Custom Data Adapter

I have built a OS data adapter off of a cube view that has a parameter that prompts for entity.  I subsequently built PowerBI query to pull data via this data adapter.  I can get the PowerBI query to pull data if I hardcode the Entity parameter value in the Custom Subst Vars in PowerBI.  What I would like to do is replace hardcoding the Entity value with list prompt for the user.  That will let the user decide which entity they want to pull when they refresh the query.  Any ideas on how to create this functionality? #PowerBI