It's not really possible to subst MediaWiki templates in VE yet (bug 49904). According to James F., it should be possible to write "subst:Foo" when inserting the template with some caveats.

This doesn't seem to work at the time. For example, writing "subst:Clarify" in the English Wikipedia, shows the string "{{subst:Clarify}}", but as a template with a highlight. When the page is saved, the template {{Clarify|date=June 2014}} is inserted - not substed.

From IRC:

aharoni: Is there a way to do a subst to a template in VE?
James_F: aharoni: Ish.
James_F: aharoni: To add a template called "Foo", instead tell it to insert subst:Foo".
James_F: aharoni: But it doesn't get the TemplateData (so it's pretty icky).
James_F: aharoni: There's a bug asking for an actual checkbox.
[...]
aharoni: James_F: about that subst thing: It doesn't seem to work. It inserts a literal {{subst:Foo}}.
James_F: aharoni: Huh. That's a regression, then. :-(

Version: unspecified
Severity: minor
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=49904