Do you need four conductors?
You may not need any additional wire up the mast.
In his book, 100 Fast & Easy Boat Improvements, Don Casey describes a way to set up two differents lights with only two wires, using a couple diodes and a double pole double throw switch. That should save you money, time, and a little weight aloft. Even if you are not a racer, every additional ounce up there only adds unproductive rolling and heeling.
I have not tried it myself yet, but Don Casey is a serious writer, so that might be a much easier way to achieve what you want.
PS: If anyone has tried this trick, please let us know. I'd like to use it to add a windex light to my rig.