windows setup with unattended.xml: unattendedjoin wrong computername

Hi
I learned the following:

To implement a secure join, add the following to the unattend file:

1. Set UnsecureJoin = FALSE.
2. Specify the credentials for performing the domain join, and the domain that you want to join the computer to.
3. Ensure that the Microsoft-Windows-Shell-Setupcomponent exists for the specialize phase. 
4. Set the <ComputerName> value to %MACHINENAME%. During installation, Windows Deployment Services will retrieve the name of the prestaged computer from AD DS and replace the %MACHINENAME% string with the actual computer name.

This works with wds 2012 and BIOS Clients.

Due to bluescreen problems with WinPE and uefi clients I'm trying to to this without wds, so my unattend.xml rests in the offline .wim.

So far I managed to get prompted for a computername, but the client would unattendedjoin the Domain not by that name but by a random name instead.

I'd like to be prompted for a computername, and I'd like the client unattendedjoin the domain by the provided name.
The client is prestaged in active directory.

Can this be achieved?