Easiest Way for Installing Filter Driver (cfadisk) within 'Boot.wim' On-the-FLY
1- First download 'Filter Driver On-the-Fly v1.0.zip' file from HERE
2- Extract 'Filter Driver On-the-Fly v1.0.zip' to any location and double-click on 'CreateDesktopShortCuts.cmd' in
order to create 'Mount_wim_2' Desktop shortcut Icon.
3- Drag-and-drop desired 'boot.wim' file onto the 'Mount_wim_2' Desktop shortcut in order to continue process.
It will automatically mount the 'boot.wim' file and copy Filter Driver files to %SystemDrive%\mount4 folder
4- You can cross-check mounted %SystemDrive%\mount4 folder for changes (not required) otherwise
Just Close Explorer (Don't forget to Close Explorer, It's very Important) !.
5- And then Enter C or D for Commit changes or Discard.
6- Press any key to Continue...
And now you can boot both 32 Bit 'Boot.wim' and 64-Bit 'Boot.wim' ("testsigning" option must be enable in BIOS BCD & UEFI BCD) within from any Partition (PTN1/PTN2/PTN3/PTN4) of your 'Removable USB Drive' in order to load 'install.wim' file within from any Partition (PTN1/PTN2/PTN3/PTN4) of your 'Removable USB Drive' in both BIOS and UEFI (Secure Boot Disable) mode.
I find this method much more reliable than using 'DISM GUI 4.0' or 'GImageX v2.1.1' or any other tools and a lot easier...