Thank you!
I will give it a try.
Currently I am testing an other solution:
e)
I used my Win10 To Go bootable USB stick and installed VirtualBox on it.
This USB windows has all the network drivers I need so VirtualBox can connect to the internet.
Then I mounted two drives:
1.) The urBackup CD iso
2.) My physical (!!!) SSD
This can be done with
C:\VirtualBoxDrives>“C:\Program Files\Oracle\VirtualBox\VBoxManage.exe”
internalcommands createrawvmdk
-filename C:\VirtualBoxDrives\raw-0.vmdk
-rawdisk \.\PHYSICALDRIVE0
Then I started the virtual machine and I got a network device, I was able to connect over the internet to my remote server and I also was able to see and start the restore to the real physical SSD outside of the VM.
Then, after a hour the throwback. Yes, it seems to work but the internet upstream of my remote place is so slow. ~2MBit/s.
So it seems that this setup works and I already reached 1% of the restore, but I had to notice that internet restore speed is way slower than the backup speed.
I think I just have to take the tablet and do the restore directly at my server’s place where the data can be transfered directly over the LAN.
But for me it seems to be a huge breakthrough that this setup basically works. With Win10 you can install nearly every driver you get and due to the virtualization the urBackup sees just a standard virtual network device that just works. 
I’m not done with this and we will see if the restore really finishes completely. But what I see right now is promissing.
BTW: I still don’t unterstand why it is not possible to restore in a VirtualBox .vhd disk container? As written in the original post, I get an error message that the “Restore partition not available.” Strange, and empty real physical disk seems to work.
For me, if this solutions really runs through, this would be the ultimative restore solution with the Win10 To Go and VirtualBox.