Oh! I got it. It wasn’t working because I was selecting views that were not of “Detail” type. Reading a little further down the forum post that I linked above I came across this bit of advice:
That works in all views when the Callouts are Detail Views/Wall Section/Building - When you invoke the Callout command >>> select appropriate type/one of the above from the type selector…
In case of Plane views, if you do not select “Detail View”, the Callout will be a “Floor Plan” associated with the original view (hence the Read Only Parameter).