There are third party tools that will let you backup just parts of files.
Pocket Backup is one.
That said, your question raises several issues:
1. If your friend is dead-set against Outlook, what PIM is he using now?
2. Is he planning to sync that PIM with the Axim's services? There may be other products that will do the sync with that PIM.
3. Is what you meant by "backup" actually syncing?