you can plug two LEDs in series straight into the Rx, i did this the other night with a glider for fun. One LED is 3v your RX is 4.8 so...
1.8 / .020 = 90 ohm resistor. it causes no interferance and i assume this is to see the plane is turned on?
the more complicted way is to open a old servo with stripped gears, de-solder the motor and draw upto .5A from here, and you can opperate it on and off from the gear switch. good fun doing spins and turning the lights off for a few seconds.
My unit does sometimes cause interferance, i don't know why
see
www.mugi.co.uk to see examples of this