Sadly, your trick does not work. When running the fake nvidia.powerd.server, as soon as I launch the SL client I get the log spammed with thousands of messages like this:
localhost dbus-daemon[1961]: [system] Rejected send message, 0 matched rules; type="error", sender=":1.23" (uid=0 pid=25669 comm="python3 /usr/local/bin/nvidia-powerd.py") interface="(unset)" member="(unset)" error name="org.freedesktop.DBus.Error.UnknownMethod" requested_reply="0" destination=":1.30" (uid=0 pid=25954 comm="./bin/cool_vl_viewer-bin")
Also, you mention that it triggers a bug in dbus itself: I am curious about this bug. Has it been fixed already (any distro-specific patch existing, if not yet fixed upstream) ?