All depends on the situation and how likely you are to die doing something else
George doesn't know the height, but as you chop the throttle, George will have to keep pitching up to try to keep on the GS, but as there is no power he will eventually induce a stall.....hopefully by which time you'll be within 1" of the runway, so in otherwords he has just flared for you.
The nice thing about the G1000 is you can read off the "numbers" very accurately. Of course
not being a Rad alt, you may find that 20' is actually -10' but assuming you have current pressure and you set it accurately, you may get away with it.
I can't try this in the UK as George lives in America
