Wait, stop and think for a while. Your contradicting yourself.
you say:
not connected to any objects and attributes.
then you go and say
I've got a list of lights and list of renderpasses, and I'd like to set on/off
relationship between any light/renderpass.
which is clearly in contradiction, obviously what your saying is that you wnat to set attributes. So if you want the easy way out then create light name attrubutes on your renderpass node, then connect them out to the real attribute, or callback and then delete the attributes once your gui is finished (theres really no reason for the attrubute not to reside here but you can do as you wish).
SHould be straightforward enough.
PyQT control
everything is possible with pyQT control.
