I don't think you could just replace the internals of the headlamp with an LED (perhaps someone smarter than me could), so I don't know if you'll be able to keep the clean look of the niterider, but you could definitely replace the head unit with Trail Tech || 35mm LEDs if the niterider uses a 10.8 volt system.

If it uses a 14.4 volt system, you'd just have to add in a 12v voltage regulator like Component - Switch: switch with 13.2V regulator & LED Indicator for HID Bike-lighting (1' long)

I'm in the same boat as I know eventually my HID light will go, and I don't want to throw away my investment in batteries and chargers.

Of course if anyone knows how to replace the head unit guts while keeping the actual head unit, I'd love to hear other suggestions.