OSX Mavericks Time Machine backup to unsupported NAS

[t80]

The trick is to configure TM for a supported local drive with a label equal to the name of your NAS share.

Use the following workaround at your own risk:

1. On a local drive, create a disk image file (change 100g to desired max size in GB. It's a growing volume, newly created one isn't that big.
hdiutil create -size 100g -fs HFS+J -volname TM-Backup "`scutil --get ComputerName`_`ifconfig en0 | grep ether | awk '{print $2}' | sed 's/://g'`.sparsebundle"

2. copy the image file to your NAS share, for example, mounted at /Volumes/NAS_backup
3. delete the image from local drive.
4. unmount the NAS share (NAS_backup).
5. Attach any local drive, supported by Time Machine, for example a USB HDD.
6. Using Disk Utility, format it to "Mac OS Extended (journaled)" and give it the name of your NAS share: NAS_backup
7. Mount this local NAS_backup
8. Set the destination for Time Machine:
sudo tmutil setdestination /Volumes/NAS_backup

9. Let TM show unsupported volumes (not sure, that this is still required):
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

10. Unmount your local NAS_backup and disconnect it (don't forget to change it's name later).
umount /Volumes/NAS_backup

11. Mount your NAS share NAS_backup
12. Go to Time Machine and turn it on.

That's it.