This can be done for about about $2-5 dollars, assuming you have a soldering iron and solder.
DIY Invisicord/Stealth Cord & Radar Hardwire - Nissan Armada Forum: Armada & Infiniti QX56 Forums
Improvised "invisicord" assembly & install tip for Radar Detector - MyG37
Just follow these steps. The wires in the mirror were different on my Z. I'm too lazy to go outside and check, but if anyone needs to know which wire to connect to I will go check.