The simplest solution is to alter the configuration of the other email clients you use. Although the server suggests default namespace and folders, each client can be programmed to use folders arbitrarily. WP8 currently has no ability to manually define default IMAP folders, but most other clients do. Note that WP8 doesn't seem to sync its "Drafts" folder to IMAP services ever.
On the WP8 device(s):
1. Setup/edit an IMAP4 account.
2. Send a test email, delete a test email, then sync the account.
3. Repeat steps 1 - 2 for every IMAP account you plan to use on the WP8 device.
On other email clients you use on other devices:
4. Setup/edit an IMAP account.
5. Subscribe to the folders "Sent Items" and "Deleted Items".
6. Configure the subscribed folder "Sent Items" as the default location to save sent email.
7. Configure the subscribed folder "Deleted Items" as the default location to save deleted email.
8. Send a test email, delete a test email, then sync the account.
9. Confirm convergence between devices by repeating steps 2 and 8.
10. Copy the contents of the original "Sent" folder to "Sent Items".
11. Copy the contents of the original "Trash" folder to "Deleted Items".
12. Unsubscribe from the original "Sent" and "Trash" folders.
13. Repeat steps 4 - 12 for every IMAP account you want to share with WP8.
