OK, I see that there are already 2 modes that you can alternate between from the way you describe. But you still have to toggle a switch to get back to your D program, and even then you only have the 2 choices on-the-fly.
What I'm suggesting is a variable mode/program where you can have all 6 (or 10 or whatever number of gradations) modes available at your fingertips via the paddles on-the-fly without toggling a shifter or switch to tell the computer how fast you want to shift on a scale of 1-6 (or 10) instead of either 1 or 5 (as in your case). And the way to achieve this is maybe to have speed/pressure sensitive paddles...
2006 330i | TiAg | Black | Al | 6MT | Sports Package | Logic 7
2008 335i | AW | Black | Al | 6MT | Sports Package | Logic 7
2013 328xi | Red | Gray | Al | 8AT | Sports Line | Premium | Executive | Heat Pkg