there is another way you can do it, and its all code compliant, but its more complicated.
you run the power there with two of the conductors (lets say black and white as line and neutral) and green as the ground
you use the red wire as a signal wire. now all you need is another switch and signal wire at the garage end. both signal wires get wired into a programmable logic controller at the garage side that is supplied with power at the garage side. you put in a 24vdc power supply at the garage side to give power to the signal wires and wire them to ground, through a standard switch, at their respective device boxes. when you hit the switch, it grounds (or ungrounds), the plc sees that as a change of state and uses that as cue to energize/deenergize an output on the plc I/O rail, and that energizes a relay that you use to control the light.
you can do it yourself pretty easily with some of the siemens plc's. but you may need someone to program it for you.
its a more industrial way to do it, but quite normal in industrial and hvac type installations. and its completely legal because your conductors are within conduit.