Sometimes this pure gold stuff can be found, like your masterpiece E2B project and this unbelievable rEFInd.
Thank you for pointing us to it Steve. Honestly.

Just to add to the WinNTSetup "tour" above, latest 3.7.5b3 added the option to include the whole DISM (x86/x64 resp.) folder from latest ADK (which you can download with GetWAIK tool by same author), so you can use DISM from WinNTSetup to add drivers to sysprep OS, before first reboot (so source ISO remains untouched).
User Atari800XL at WinNTSetup thread at MSFN forum describes his smart strategy on this. He keeps different ISOs in his UFD with different driver sets. Depending on target system, he mounts one of the ISOs and uses WinNTSetup to slipstream drivers on sysprep OS. He showed a commandline sample:
run,q:\winntsetup\WinNTSetup_x86.exe nt6 -source:y:\os\w7.wim -syspart:c: -unattend:"autounattend_w7.xml" -savedriveletters -sysletter:c -reboot -disableuac -drivers:L: -runafter:"CopySetupScriptsW7.exe"
where L: contains the (ImDisk) mounted drivers ISO.
Actually before b3 WinNTSetup used DISM from source OS ISO, but after some debugging last days, author offered option to use DISM from WinNTSetup Tools folder for reliability reasons.
Thanks again for rEFInd, sir.