Now this is high-fucking-tech...

Duct tape and bailing wire pretty much literally, so endoscopic tools with embedded six degree-of-freedom sensors (Ascension Tech). The magnetic tracking isn't without some headaches, but so far I'm pretty impressed with the precision. As expected metal screws with them, but a bit unexpectedly, the accuracy varies dramatically depending on where in the magnetic field volume the sensor is-- get too close to the emitter and all is lost.