We all know the limitations of a large Install.wim on a FAT32 USB Drive, you can't copy the Install.wim if it is larger than 4GB. This is a limitation of FAT32, but FAT32 is required for UEFI Boot!
Export Image Index from the Install.wim
The most common method is to implement because the odds are, you have a multi-Index Install.wim
Simply export the Windows Image Index that you want to use and copy that to the Sources directory on your USB Drive. If you do need multiple Indexes on a USB, this probably won't work for you
It is also possible to make a multi-Partition USB to use a FAT32 and NTFS structure.
Brooks Peppin does a great job with his script for creating a 500MB FAT32 Boot Partition and using an AutoUnattend.xml. Give him a follow and a read on his blog for a good How-To on this method.
Solution: Split the Install.wim
The easiest solution for a large Install.wim to use with Windows Setup is to split the Install.wim using Split-WindowsImage
You can then take the SWM files and place them in your Sources directory instead of having a single Install.wim. There is no need to edit any files, or to make any other changes, Windows Setup already looks for an install.swm file
Does it really work? Yes.
OSDeploy PowerShell Module
If you are looking for an automated way to create a USB with SWM files from an ISO, install the OSDeploy PowerShell Module and useCopy-IsoToUSB with the -SplitWim parameter. This parameter will be set automatically if you are creating a FAT32 USB and the Install.wim is larger than 4GB
The process to split the Install.wim takes a little longer than a simple copy since the SWM files need to be generated, so give it some time. These are the steps that are required
Copy Install.wim to Temp
Remove Install.wim Read Only Flag (cannot Split if this is set)