It's doable, you'd probably need a change over relay (double throw) for each side linked into the indicator switch so it cuts the permanent power when indicators switched on, probably not legal in UK though.It's pretty much how the USA imports are as standard but I can't remember how they are wired, many years ago I got a USA Z650 for swmbo that worked as you say but I'm buggered if I can remember how I changed it back to normal, I thing it was all in the loom and just cut the sidelight wires but not sure, so if you can find an old yank wiring diagram it may help.Check the law first though.