Drivers signing problem adding to WDS

Hello

I need to add NIC (Intel Ethernet Connection I218-V) drivers to my WDS boot image (Windows Server 2008 R2)

I tried to add a driver to WDS drivers, but WDS refuses to add it saying the driver is not signed.

I installed the same driver on my workstation and it appers in driver properties, it is signed by Microsoft Windows Hardware Compatibility Publisher.

So why WDS refuses to install them?