James, I'm not sure where the rectangular hole came about... I was referring to coring a common 2-1/2" (62mm) diameter hole (cavity) into the driveway or walkway, removing the core so you will have a nice sleeve to work with. You would then tunnel under the concrete with a fish stick or fish tape and pull the fixture wire out towards the side. I would then mix some quick setting cement.. pour it in and install the fixture. You would have to carefully press the fixture down until the lens is flush with the surface, and wait till the cement sets up. In the meantime, you could do your hookup and continue. About the conduit- You could install a length of 1/2" flexible conduit under the cement and out towards the edge, however most cement is poured on aggregate and that would snag the conduit, making it harder to push it through. You wouldnt want to over excavate or undermine the driveway. We use the fast setting cement because that will fill any voids you create.