Windows Server 2012 R2 Essentials - no RDS-Virtualization

Hi,

I'm currently customizing the Windows Server 2012 R2 Essentials ISO for installation of Hyper-V-Role on Host and included VM with all Essentials-Roles as per http://technet.microsoft.com/en-us/library/dn293253.aspx

Now I would also like to include the feature "Remote Desktop Virtualization Host" on the Hyper-V-Host, so I can have Windows7 or 8/8.1 with RemoteFX in a second VM. Command should be

dism /Image:C:\essentials-host-mount /Enable-Feature:RDS-Virtualization

but this feature doesn't seem to be included in the image at all. Is there any possibility to integrate this feature (eg. ripping from a Win2012R2-Standard-Iso)? And will I have any licensing issues? Or will I have to use Windows Server 2012 R2 Standard for RDS-Virtualization / Remote-FX?