"DOpusInstall.exe" have relevant command line parameters?
[Edit: This probably doesn't work, until we update the guide. See the post below.]
Near the top of the FAQs:
I just realised that guide probably only works with the InstallShield installers, and we recently moved to InnoSetup. The guide most likely needs updating for the newer installers.
This page looks like it has the command line arguments you would need for the newer installer: