To verify, the goal is to set the email argument for each user, for each interactive app, in a single place.
What resource manager are you using?
Out of the box we don’t support this, but we have discussed adding support for this type of thing, as we would find it very useful as well. These are some related issues we have currently opened up:
I’ll add a reference to this from the first issue mentioned.
There may be some work around’s that might be sufficient for you. For example, in a custom Rails initializer you could add some code that sets default value, using monkey patching. But this is not necessarily reliable to work between versions of OnDemand.