Hi I just noticed this question when I was searching for something else. I am not sure if you found your solution or not, but the best possible way that I know is to build your WinPE using (now moving forward BartPE is way old)
WinBuilder, simple google should find it for you. http://winbuilder.net.
The other alternative is to build using
Either of these will be fine. alternatively if you don't want to make it from scratch you can mount an existing WIM using a utility called gImageX which is AutoIT built GUI to edit WIM images. All of these will require WAIK (Windows Automated Installation Kit) free on from the Microsoft website.
WinBuilder you don't need it as such as it will download what it needs from WAIK and then you can build. Which ever way you go, you will need to insert a simple exe called
It is very simple and easy to use. Google of all of these things should set you going pretty easy. Worst comes to worse I can make you an ISO that you can burn that will allow you to boot into WinPE to make you an ISO from your system.
Lastly you may want to skip all of that and backup your system to a WIM image. This is something I have never tried myself so only going off what I have read. You generate a WIM (from recovery) and then convert it to ISO later. To do this you need to edit a WIM file add gIMageX into you WIM and then make this into a bootable WinPE. Then record your system to a WIM image and then once back into the system create a ISO from the generated WIM via this command:
oscdimg.exe –bC:\expandedSetup\boot\etfsboot.com –u2 –h -m -lWIN_EN_DVD C:\expandedSetup\ C:\Windows 7.iso