Hack idea for someone to try (I can't as I have the Hosted Domain setup, we don't have IMAP rolled out to us yet):
1) find a random IMAP server to configure in BIS that is *not* gmail (if anyone knows of free IMAP email services for this, pipe up!)
2) after completing config, go back and edit the account in BIS to be your normal GMail login - I'm thinking that it won't check if you edit *after the fact* a gmail account
What I'm curious is if you can short-circuit the BIS logic during initial setup by using a real IMAP-non-Google account, then going back and shoving in your gmail credentials as an IMAP setup instead of the auto-detected gmail.
Give it a shot, let us know.