I have dealt with many of these letters on behalf of my company. Our performance engineers determined that we cannot follow the VMC departure procedure due to obstacle issues, so we always follow the IMC procedure. This does not cause a problem with Unique.
What Unique wants is the aircraft to start a turn at 2400', not 2700 or 3200 or whatever. 99% of the problems were caused by crews not starting the turn as soon as they get to 2400'. Since every departure will have a unique point at which it will achieve 2400', there is no hard and fast geographic point at which you have to turn. A lightly loaded 767 will achieve 2400' much earlier than a heavily loaded 340-300. Unique understands this, so the clock starts ticking once you reach 2400'..if you delay your turn X seconds after achieving 2400', you'll get a letter.... What X is, Unique won't tell, but it is in the order of 10-15 seconds.
As far as I know, no one has been violated for not following the NADP. It's always a track/lateral error.
And as has been pointed out, one has just use heading select or the equivalent mode to get the turn going and use heading mode until west of the airport. Using LNAV will definitely get you into trouble.
If one gets a letter, don't be a jerk, just answer it honestly and that will probably end the matter...