I have a suggestion: can you run Finisher at T-0? This method must be used with driverpacks method2.
I mean, when windows' setup.exe ends, just before rebooting to first logon, this is T-0. the fake setup.exe's current behavior is something like:
start /wait "%systemroot%\system32\setup.exe" -newsetup
exitprocess
so we can insert command before "exit" and don't let fake setup.exe end, like this:
start /wait "%systemroot%\system32\setup.exe" -newsetup
%systemdrive%\DpsFnshr.exe
exitprocess
once setup.exe is not ended, the machine won't reboot(Not sure but I know the vice versa is true: once setup.exe is ended, the machine reboots.)
Additionally, a postsetup.cmd(make it 8-3 compatible plz), or something like this is great, we can run something that cannot be executed at T-13, for example, dot net 3.0 installer, because the requirement of dot net 3.0 is complete at post-T13 stage(font caching).
----edit----
I'll try using 7z sfx to replace the real setup.exe, making it a 2nd-fake-setup.exe, to see whether it works.