I don't think there's a generic ActiveX container that will allow you to load anything into it.
What you might look into is SubPanels. If you create a SubPanel on your
main VI, you can create a subVI with the approprite ActiveX container
for each document type and load the subVI into the SubPanel as needed.
I don't have any examples of this, but if you look through the Example
Finder, you can find both SubPanel and ActiveX examples that ship with
LabVIEW.
Ed