How to auto-subscribe to virtual namespace/prefix?

In virtual namespace I can have:

namespace myvirt { location = blah prefix=Virtual/ separator=/

mailbox "My folder" { auto = subscribe } }

And i see email clients successful display subscribed "My folder" but the top-level prefix "Virtual/" is not subscribed. I see the Virtual/ prefix available as a noselect folder in the list of unsubscribed folders and if I manual subscribe to it, folder tree display is perfect.

So how can i also make auto-subscription to the "Virtual/" prefix noselect folder?