Can't we just download a copy of the apk for Gmail. Rename it to Gmail2 or something, then install it? Would that work to give us a 2nd gmail app?
And in regards to signing in with a different account: you can use AnyCut to make a shortcut to the setup wizard, which allows you to go through that process again. not sure if it wipes your data or not though. Don't know if this still works in jf adp 1.5