Hi Don,
Over on BMWMOA, I noticed you were asking the same question about adding the RT fairing and observed the same cable length limitation. One of the suggestions was to purchase wires of different colours to extend the harness, and try to get the same as stock. Generally, that is a very difficult task to accomplish, but there are a couple of possible creative solutions that will help when extending the wiring, as you've mentioned you need to do.
1) purchase a very cheap harness from eBay to cannibalise. They are our there. You can choose one that's been damaged since you're going to cut up anyway for the wires.
2) Introduce the wire splice midway. For any given wire that you intend to lengthen, clip the original wire partway down from the connector to expose 5" - 6" of wire lead on the connector. Then strip both ends and solder in the lengthening splice. The chosen wire can be of any colour but must be of the same gauge. Use solder and shrink-wrap over each joint. Try very hard to stagger splices so that the overall thickness of a group of wires remains small. When finished, wrap up the cable with tape. This method will mean you always have the correct wire colour at both ends.
Below is the best way to splice wires.