TBH, I would not bother if it is just a detector. A Laser gun takes less than a second to get a reading, all it will do is tell you that you have just been caught.
If you mount it on the dash you might get lucky and it picks up some scatter from the car in front, but unlikely I think.
Anyhoo, I think the way though the bulkhead is to lift the plastic scuttle panel on the battery side and there is a gommet to the right of the silver ECU box. I believe that if the glovebox is removed, it should be possible to get access in the cabin. But there is the issue of disconnecting the airbag switch in the glovebox which will trigger an airbag fault light. So I suspect disconnecting the battery during this operation may be a good idea.
I hope to confirm this route in the next few days, as I need to get a cable though as well.
