I was able to do this by going with method 2, then
- copy presetup.cmd and setuporg.exe to <yourosdir>/I386/$OEM$/$$/System32
- copy the OEM directory to <yourosdir>/I386/$OEM$/
- Delete the lines in txtsetup.sif that refer to setuporg.exe and presetup.cmd (I had problems with this, not sure why)
- Add a line in your base.bat to launch DPsFnshr.exe (like Adrien says)
- Add to scripts/unattend.txt:
[GUIRunOnce]
command9 = "%SystemDrive%\DPsFnshr.exe"
There may be some extra steps, but thats how I got it to work and it was much simpler than previously. Thanks, Adrien, for pretty much solving this issue for me.