Windows ICD Hard Drive Partitioning

I have created my Windows ICD Build that I am deploying and it works, but I have one thing I need to accomplish. I want to partition the Hard Drive into a O/S partition C: & Data Partition Z:
My initial thought was to boot the target computer with a WindowPE flash Drive and use Diskpart to partition the hard drive prior to running my Windows ICD Flash Drive build installer.
Currently the Window ICD Installer completely wipes the hard drive and installs the O/S with my Customization's (completely unattended). What I want is for the installer to leave the Data Partition (Z:) untouched. There will be files within the Z: partition i need to stay if or when we need to rebuild the computer using the Windows ICD installer. Is there a way to make my Windows ICD build just install to the c partition and not overwrite the z: partition? I need this partition to remain after every rebuild

The only problem is that I want to keep the data in Z current at the time of rebuild. If I image the z partition it will only restore the image that was taken and not the current data in the partition.

I read somewhere that the option to create Production Media (as opposed to Clean) gives more options to add test scripts so maybe other scripts could be added in that option? I really don't know though.

This page also suggests you can save your image as a FFU file (I never got that to work but haven't tried since ADK 1511) and then deploy with a DISM command, which presumably gives more control if you change some of the DISM parameters(?) But it's not as user friendly as inserting a bootable USB stick and letting it run.
Lab 1: Customize and install Windows using the Windows Imaging and Configuration Designer (ICD)

Step 9: Install Windows on the reference device

1. Insert the WinPE USB drive into your reference device.
2. Boot up the reference device to the boot device selection menu. You usually do this by powering on the device and quickly pressing a specific key or button (for example, the Esc key or the Volume down button), and selecting the USB key.
3. Insert the FFU USB drive into your reference device. Determine which driver letter is assigned to this drive by doing the following:
   
   1. From the WinPE command prompt, type: diskpart and press Enter.
   2. At the diskpart prompt, typelist volume and press Enter.
   
   This lists all of the volumes present in the system. Determine the driver letter that corresponds to the FFU USB key, for example, G.
4. From the WinPE command prompt, type the following:

Code:

Dism.exe /apply-image /imagefile=G:\MyFFUImage.ffu /applydrive=\\.\physicaldrive0 /skipplatformcheck /logpath:G:\dism.applyffu.log

Where G:\MyFFUImage.ffu is the file location of the FFU file.

These computers will be going to a customer site, where they will not be performing any backups and we wont have access to do either. We will provide them with the USB Installer Flash Drive create by us with the Windows ICD. Currently this install wipes the entire hard drive and silently install everything back, which is my basic problem. I just tried running WindowsPE to partition the Hard Drive into the partitions before using the USB Installer. I create the 2 partitions, but the Windows ICD flash Install still overwrites the entire disk and I lose my z partition. Maybe there just isn't a way to do this through Windows ICD. I am going to submit a support ticket through Microsoft to see what they provide.

I'll be interested to see what they come back with.

They created a case, now I am waiting for a contact. I will update here if/when I get some help.