As an alternative to adding the control at runtime...
I ran into the same problem. I overcame it by hiding a calendar on a 'common' form (never gets displayed) and using formlib.changeParent to move the calendar to whatever form I needed it on. When the form is closed, the calendar gets moved back to the 'common' form (again, via formlib.changeParent).
Naturally, this has the disadvantage that only one calendar is available for this purpose at any given moment... but I suppose that two or more would be possible. I just wouldn't want to code it.
Gary