What exactly are you trying to achieve?
The WinPE boot system is 32 bit, so adding 64 bit drivers is pointless. Deploying a 64 bit image generated by Ghost can be done using 32 bit WinPE. The only time that you need to boot 64 bit WinPE is when you are going to run a scripted (or manual) install of a 64 bit operating system from the original media.
Or have I totally misunderstood your question?