Adding backup from loaner device on BB9900

I have a BB9900 which I need to send for service, I will be getting a loaner BB to use in the mean time.

I made a backup of all data and apps and will wipe all data before sending it.

My question is , how can I backup data from loaner BB after I use it for 1-2 weeks and add this data to my BB 9900 after I restore my original backup/apps ?
I want to have all the data from loaner device on my BB after it comes back from service, but I also want to keep all my original data as it was backed up.

Restore the backup from your actual phone to the loaner, use the loaner as you would your normal phone.

When you get your phone back, backup the loaner and restore to your phone.

There is no simple way of merging two backups, and restoring a backup to a phone will overwrite the data rather than merge it.

That makes sense, I should have thought of that :p Thanks