To build drivers you will need only the EWDK. Run the EWDK LaunchBuildEnv, navigate to a driver source directory and do:
buildme.cmd
Copy contents of \drivers and \winpe_stuff to \Windows\system32 inside \sources\boot.wim of a WinPE image.
You will need to enable test signing in the bcd. E.g.: bcdedit /store K:\efi\Microsoft\boot\bcd /set {default} testsigning yes