Theory states that this is not just a sound reduction exercise by BMW. It is a simple fact that reducing the overall pipe diameter at lower revs increases low end torque.
This theory ties in with the behaviour of the valves (on my F10 M5 at least). With no 'mod', they are closed at cold start up, then open after 90 seconds or so. From then on, at idle, the valves should always be open. There is no need for torque at tickover and the car sounds better with them open.
They then close as you move off and drive at low/med revs, and then open again under WOT or high rev conditions.
You can use zip ties to keep them open. Much easier than wiring, and they won't wear through/corrode like wire. The melting point of nylon is almost twice that of the max temp of the exhaust tips, so they won't melt. I've had mine on for many a lap of the Nordschliefe and they still look brand new. (approx 270 degrees C for nylon vs 150 degrees C for your exhaust tips).
If anyone is near a dyno, and can be bothered to check the low/mid range torque with valves open and closed, then we can put this to bed once and for all. I don't think I can tell, but it's hard to be 100% certain. We need some numbers
