Google Docs has an API that allows you to search, download, delete and retrieve documents from the list of Google Docs for a specific user, you could use this to download a document from your server, and then get the URL of this document (after importing it), which can then be used to redirect the user. It would not be as smooth as Gmail integration, since you could not show this fancy page "Importing your document ...", but that might be enough.
As for the other observations, I do not know anything.
Daniel Spiewak
source share