[Dovecot] Multiple Maildir?

[Marc Perkel]

OK - Getting close to everything working in my weird configuration. 
Here's a problem I'm still having.

I'm authenticating with this:

userdb {
   driver = sql
   args = /etc/dovecot/master-combined-sql.conf
}

Default mail location:

mail_location = maildir:/fakedir/%d/%n:INBOX=/email/%d/%n:LAYOUT=fs

However - what I'd like to do is if the mail location doesn't exist then 
I want to try a second mail location:

mail_location = maildir:/email/%d/%n:INBOX=/email/%d/%n:LAYOUT=fs

How do I do that? Thanks in advance