Voltage Detection Modules?

[genltd]

I'm am trying to retrofit an leviton/hai omni into a listed building (an old church). The problem is for the lower level I'm not able to drill holes anywhere and all the existing wiring is inside the stonework somewhere, yet I need a way of detecting occupancy.
 
Since there are no windows in the lower level, lights are a must, so my only workable idea right now is to tap into the wiring between the switches (at ground level) and the lower level, add a bunch of relay's and use the contacts as zones to show which lights are on. The wiring is the really old stuff with mica insulation so I'd rather have something that doesn't require me to actually cut into it, like some sort of proximity solution. Anyone any ideas? 

 

[BraveSirRobbin]

The RIBXGTA module requires no power, a split open core that will slide over an existing wire without disconnecting it, and provide a threshold adjustable current sensor trigger that will provide a contact closure.
 
But, I have to ask, you must have access to 'some' sort of wiring based on your statement of wanting to use relays (i.e. you have to get those contact closures to the panel via some wire).
 
So my question, not knowing your entire situation is, why not use a more conventional detection method if you have access to wiring that leads to the panel?