Downloading IMAP folder content for offline use, but *not* syncronizing

Is it possible to use PTB in IMAP mode, download all content for offline use, but *not* have it syncronize? (ie - delete from PTB any emails that have been deleted from the server?)

I have users who normally use webmail, and have created multiple folders and filters via the web interface. Now they would like to archive to PTB, and then remove the original emails from the server *without* deleting them from PTB as well.

And then at some unknown date in the future when they've got another 1000 (or so) emails on the server that they want to archive, download those to PTB and the respective IMAP folders without deleting the emails on PTB that no longer appear on the server.

Is that possible? It needs to be as simple as possible - some of these people still need to be reminded to turn off Caps-lock when checking their email.

Thanks!

Mark