How to supervise an unsupervised iOS device keeping the users Data? I'm pretty new to the whole Apple story, so i'm not sure if this is possible at all.

The story is that we have unsupervised corporate-owned iPhones at work. Now we are about to enroll an MDM (specific MobileIron) and the devices need to be in supervised mode.

What we tried so far:

Backup the iPhone (iTunes), supervise the device in Apple configurator 2, and push the backup back onto the iPhone. 
Somehow my Instructor managed to get it working: the iPhone was now supervised containing all user data.
New day, new iPhone, he did all the same steps again (iTunes and iCloud Backup), an reproductibly we couldn't get the backup back to supervised mode. We've tried it with 3 iPhones 5s and on one iPad mini 2, it was either wiped and supervised, or it was only the unsupervised user backup. 

I've been searching https://discussions.apple.com and other boards since last friday, no success so far. What i found were instructions for new, wiped devices, which didn't help.

My last hope is that you can help me solving this problem. 

Is it possible to supervise a device without wiping it and restoring or keeping the users data for it?

Thanks folks!
According to this discussion thread, you can try the following method:

WARNING: I have not tested this and you may lose data!


  
  Disable "Find my iPad” on the old iOS device, perform iCloud backup on the same device
  Plug in the new device to Apple Configurator, Supervise and update the device to the latest iOS
  Once Supervised, unplug the new device and go through the Setup Assistant to restore from iCloud
  When the iCloud restore of the new device is complete, do not touch the Setup Assistant, plug it back into Configurator
  Before you refresh, change the "Restore" and "Update iOS" options to "Do not Update/Restore"
  Once refreshed, proceed through the Setup Assistant, your device should now be Supervised and ready for MDM Enrollment
  


Note that this is for cloning a device, I have not found a way to use the backup of the same device to supervise it.

Also, it does appear that you can try this with an iTunes backup as well if you'd like. Just follow the same steps and use iTunes instead of iCloud to get a more complete backup.

It looks, however, like some versions of Apple Configurator do and do not work, so your mileage may vary.