I have changed the way the lighting works in my tails, but I eliminated functions as opposed to adding.
My guess would be you need to identify the brakelight lead and tap into it, then add a wire running from the tap to the plastic port the bulb plugs into where you want to have a brake light.
I don't know if the port you want to add brakelight capability to will have a space to add the new you added, you may need to replace this port with ones your existing brake light bulbs plug into. Or if you don't care about keeping the parking light function in the inner tails you could just identify and cut the dim lead and put the brake lead wire you added into where the dim was.