, it's somehow limitation. However, there are number of ways to copy files/folders during setup using:
A command or batch script in/called from
5. SetupParams in winnt.sif
6. GUIRunOnce and RunOnceEX in winnt.sif
could be a good place for reference.
About the limitation- in my tests I could not prevent Setup attempts to install on USB drive, when even a single line in [unattended] is present.
If there is not required space on USB drive you are lucky- you get an error message and can change partition, but if there is- Setup installs windows on the USB drive, usually changing the bootsector, which we do not want. That's why we remove the whole [unattended] section.
From ref.chm [data]:
Installs Windows to the first available partition that has adequate space for a Windows installation and does not already contain an installed version of Windows.
AutoPartition = 1
Either omit the AutoPartition entry from your answer file or set the value of AutoPartition to 1. If AutoPartition = 1, the /tempdrive command-line option of Winnt32.exe is ignored during Setup. If you do not set the value, text-mode Setup installs Windows on the partition where $WIN_NT$.~LS is located.
But even with AutoPartition = 0 or without this line, the presence of $WIN_NT$.~LS and
any data in [unattended] seems to trigger Setup not to ask about destination partition. If someone finds a better way I'll be more than happy to use it.
About the 0X0000006B message- honestly I have no clues, apart from bad file during copying from hard drive. Do you amend winnt.sif in the same way when source is virtual CD and hard drive? Does the path to USB_MultiBoot2 folder contain spaces? I think Wimb fixed that already and you may need to redownload USB_MultiBoot2.cmd.