I struggle to shoot properly when wildfowling!
Kneeling down, admittedly, is not the ideal position from which to mount and swing a gun but it is something that becomes easier the more you do it.
As such you could do a lot worse than practice dry mounting at home, on your knees, and learn how to shuffle position in order to keep your gun muzzles aligned to the line of the imaginary target you’re swinging on.
Think in terms of having had your legs removed at the knees and practice positioning yourself to face the direction of the shot by placing your leading leg (sorry, stump) in front of the other.
Finally, don’t fall into the habit of using just your arms and shoulders to move the gun – the power to drive it needs to comes from rotating from your hips and upper chest.