Whle it may be true that you can fly below green dot clean, the question remains why would you want to? Flap 1 for a few track miles will not affect your fuel burn to any measurable degree, but it will preserve your manoeuvring buffer.
Consider the following: 15 kts below green dot, levelling from a descent, turning with 30 deg AoB, turbulence (either wake, thermal or shear). Your protection speeds will increase substantially coupled with a sharp decrease in airspeed. Result: Alpha floor!
Why anyone would want to reduce their manoeuvre margin is beyond me.