First of all, those types of LEDs aren't going to be bright enough or have a wide enough dispersion pattern to be useful IMO. LEDs are pretty directional. There are 1W and 3W LEDs that will work better for what you want. You can get the 3W LEDs from various places, but it might be cheaper just to get a couple/few of
these and take out the parts you need.
And no matter what voltage the MMM BEC puts out, you are going to want to use an LED to limit the current or it'll blow. Since you are going to use 2 or 3 LEDs, put them in series (along with the proper resistor) and run off the main battery pack. More efficient this way and won't load the BEC for nothing.
Then, you are going to need a switching device to convert the pulses on CH3 to an on/off signal. DimensionEgineering has such a device:
http://www.dimensionengineering.com/PicoSwitch.htm