Fire up the WinPE ISO made earlier, make sure NOT TO BOOT the regular HDD or you will have to restart.
Now using the CLI you need to mount the system partition and create the image.
Now you need to extract that file from the VM, there are many ways so I leave that to you. Personally, I fired up a LiveISO and copied the file to a network share.
Note: You can just fire up the VM, the whole reason for not booting the HDD before doing this is it will setup the system just like the custom ISO would, but you need to capture the image BEFORE that happens. After you create win10sys.wim, you can just fire up the VM and copy the file from C:\win10sys.wim to your host computer via network share/whatever. It's also a good test of what an installed system would look like with the install.