A boot image has been uploaded to SCCM that is the WinRE.wim found in Windows 11 System32\Recovery. This wim includes support for wireless when in PE environment.
There are 2 files injected into this wim in C:\windows. Called wlan.cmd and Wifi-CRS-TS.xml.
Files can be added/removed and modified by mounting the wim image via dism then unmounting when finished.
Mount example
dism /Mount-Wim /WimFile:C:\mount\winre.wim /index:1 /MountDir:C:\mount\wlan /Optimize
Unmount example
Dism /Unmount-Image /MountDir:C:\mount\wlan /commit
This was the key, editing the winpeshl.ini file in C:\windows\system32:
By adding the location of the script it will run before the task sequence login screen
A task can be added to the TS to remove these files at the end to clear up.
Adding this boot image to SCCM, or modifying it when it's already in SCCM using the built in tools, modifies the winpeshl.ini file >:(. Currently im getting around this by replacing the boot.wim in the Sources file on the USB stick once it's been "rufus'd". The location of this boot.wim is in \\crs-sccm-01\content$\intune\boot potential cause below?
Config Manager Boot Images not working after site upgrade to 2111 - Microsoft Q&A