This is where small spending needs to be done. Look at http://www.datamills.com/products/edgesafe-pst2pst-backup – precisly solves your problem of backups during noramal Outlook operation in incremental manner
This is one option.
Microsoft Outlook Personal Folders Backup tool
Here is how it works.
User closes Outlook
Gets a popup asking if they want to back it up.
It creats a backup pst file.
The backup pst file can be backed up since it is not active.
BackupMyFolder! -> Free and for single user. It backs up your PST(s) while OL is running or not and it manages incremental.
PSTStation Corporate does exactly the same but for Entreprise. It manages PST backup from a central location, even if Outlook is opened on remote workstation and does incremental.
Both solutions are delivered by AddOnMail.
Restoring outlook files is easy with the help of corrupt .pst. The application uses modern methods of restoring. The utility demonstrates the results of working with invalid .pst files.