Browsing the setup files folder you may found the following:

.\eXpress\Deployment Server\Deploy\WinOSXXX\sources\sources\$OEM$\
                $1\DAgent\DAgent.msi
                $$\Setup\Scripts\setupcomplete.cmd

Move the $OEM$ folder with all its content one level up and disable UAC.

Make sure that the path typed in the setupcomplete.cmd is pointing to c:\dagent.msi

You can disable UAC by editing the unattend.xml file:

<settings pass="offlineServicing">

<component name="Microsoft-Windows-LUA-Settings" processorArchitecture="amd64" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<EnableLUA>false</EnableLUA>

</component>

</settings>