I was able to figure everything out! It required quite a rewrite of what I did for 4.0.4 to adapt it to 4.1.0 but now I have a functioning Qubes 4.1.0 OEM install disk that will prompt you post-install for your LUKS unlock password as part of the user setup.
Now we will test it some more internally before starting to use it for new Librem orders that request Qubes.