Using deluge in report filter

Using deluge in report filter

I'm trying to create a report filter that looks up a value in the user profile.  But when I add the function to the report filter criteria, Zoho keeps adding quotation marks to it.  I enter Container_ID starts with thisapp.get_user_containers(), but when I save it becomes Container_ID.startsWith("thisapp.get_user_containers()").  So it's looking for a constant instead of running my function.

Any ideas how to stop it adding the "" in the report filters please?