I know what you mean. i am using this technic too, but only when there is a danger of a windshear.
First choice of course is to avoid WS and delay a T/O.
The procedure I am using is:
First I calculate the actual weight and use a optimum or lower flap setting.
The MATOW from there I use for a new calculation and use the same flap setting as above.
This way you are safe in regards to your Vmcg.
Now I am using the speeds from the first step and remember the increased Vr speed.( The performance limited Vr speed ) I rotate normal at the increased Vr speed and aim for the increased V2 from the MATOW calculation.
But if the runway is contaminated you got to use Full thrust or use Derated T/O thrust. In either of these cases, you can not use this procedure.
Dutytime regulations.
Good point Gulfstreamaviator
These regulations are made for us pilots and we should stick to them. I know very well how hard it is to say:
Sorry I got to sleep now for 10 hours.
Better you hide yourself after saying it via PA.
Especially if you got 300 people in your belly already waiting for hours in the a/c.
#2 - Your company is pushing you to fly and you got to explain yourself, why you are not flying. Did happen of course to me too and I already had some discussions about it with my scheduling.
But we shouldn´t forget, if something happens, it is up to us.
Who has to face the judge and explain why people got hurt on that flight.
Good if nothing happens, but better not to challenge our luck.
I think we can give a little, but we still got to stay within a reasonable limit and should not stretch the law to far.
Imagine getting to HKG and someone gets hurt after 16:10h dutytime.
The attorney confronting us, will rip you in pieces at court.
Had a friend at court in the U.S. because a PAX got hurt in turbulence in U.S. airspace and she had her seatbelt not fastened ( Seat Belts Signs ON ).
That really gave him many sleepless nights. But this is a different story.