There's a couple of places you can pick up battery voltage closer to the front of the bike. The first is the battery indicator lights if you have them. The wire to them is battery voltage and they use the throttle ground as the negative. You could splice in to those two wires. That would be very convenient if your throttle has the red button, which you could re-purpose. Each LED is about 2.5A at 3V, so 4 LEDs would be 30w or nearly 1A from the battery, which is probably a bit much for very thin throttle wires
The other place is the LED or LCD control panel. It's powered by battery voltage, so has both wires that you can splice into; however, you have the same problem that the wires might be too small. They'd be OK for a single LED light, but those ones above take a lot of power