CG2 is common ground, so just take any + and wire it to the + of each of the leds (cut the traces for the + first)
ya but it is CG2 and power is on all the time....
On CG1 the LED needed a positive voltage to activate like kicks suggested so with CG 1 you would apply the switched 3V supply to the LEDs to activate when the controller is on. However CG2 is like matrix in that the power source used for mods is not switched on and off with the controller, I believe when controller is off the +V is battery voltage.
so just like matrix you need something to use as a switch to only apply power when the controller is on. you can use an opto coupler or a transistor, however the key is finding a spot that provides the switched signal to tell the device to turn on and off.
In the top of this board there is a stickied topic about switched power in CG2 controller written by RDC that would be a good referance for this mod.