You are close to get it.
“lifting one's legs at the hip without bending one's knees will create a "control" input that will have a "downward" pitch effect enabling transition to forward flight.”
Let me explain a little further your “control input”.
Suppose that initially the Portable Flyer is hovering, with the thrust force vectoring upwards and passing through the overall center of gravity.
By lifting his legs at a normal angle relative to his spine, the pilot varies the eccentricity of the center of gravity relative to the thrust axis (actually, what the pilot does is to shift the thrust axis offset to the overall center of gravity).
With the thrust axis offset from the overall center of gravity, a torque (or moment) is generated (it equals to the thrust force times the offset of the overall center of gravity from the thrust axis); this torque accelerates angularly the Portable Flyer (including the pilot); even a tiny torque will accelerate angularly the Portable Flyer, however the smaller the torque the weaker the angular acceleration.
As the thrust force turns forwards (pitch effect), the horizontal component of the thrust force accelerates the Portable Flyer forwards (in order to keep his altitude, the pilot has to open properly the throttle).
If the pilot keeps his legs at normal angle relative to his spine, the Portable Flyer cannot stop turning (it will turn upside-down, with the thrust force pushing downwards), which is a problem).
So how things work?
When the leaning of the thrust axis is adequate (for the desirable forwards flight), the pilot restores his legs at their initial position / posture (say, in line with his spine), eliminating the torque.
But this is not adequate.
If he does so, the Portable Flyer stops accelerating angularly, but continues to turn at constant angular velocity; so, what the pilot has to do in order to stop the rotation of the Portable Flyer is to apply a decelerating toque (say, by bending his knees or by bending his spine).
To return to hovering, the pilot has to displace the thrust axis upwards, and he can do this by changing properly his body posture. Same reasoning as above.
To turn to backwards flight, the pilot has to vector the thrust axis backwards, and this can be done by, say, properly bending his spine and / or legs.
Similarly for side-wards flight: if the pilot lifts his left leg to the side, the thrust axis turns to the left etc.
And what about the yaw control?
The pilot of the Portable Flyer is permanently, from taking off to landing, into a high speed air stream. By deflecting a part of the air stream, a pair of forces causes the rotation of the Portable Flyer about its long axis.
Suppose the pilot turns for 15 degrees his left leg forwards and for the same degrees his right leg backwards. The reaction from the deflected - by his legs - air is a pair of forces that accelerates the Portable Flyer about its long axis. This is the yaw control. If the pilot turns his legs the other way (the left leg backwards, the right leg forwards) the Portable Flyer yaws at the opposite direction.
Do you know the following “paper toy”?
If you throw it, it turns like a helicopter rotor.
The two wings of the toy are the legs of the pilot, the rest toy is the body of the pilot.
This is what the skydivers do in order to yaw:
According the previous analysis, if the pilot is lifting his legs at the hip without bending his knees, the torque (“control input”) will be so strong that the Portable Flyer will turn too fast.
More reasonable is the pilot to bend slightly his legs; this creates a “control” input and is easy for everybody.
If something is not clear, please let me know to further explain.