Utility-sized cables, or alternatively a separate sense wire to measure the voltage on the other end of the cable. This would allow you to adjust the output vol

Utility-sized cables, or alternatively a separate sense wire to measure the voltage on the other end of the cable. This would allow you to adjust the output voltage of the power supply to deliver the required voltage, including the voltage drop over the cable, and your LEDs would work just fine. At least as long as the cable doesn't catch fire from the resulting power dissipation...