Denis,

I use a logitech gamepad quite often. I know of no way to stop the
throttle from auto centring short of physical modifications that would
mutilate it and take several broken gamepads to get right (if you can).
If you work out a better way let us know.

I use the 2 buttons on the front of the controller for a throttle. One
to increase and one to decrease. It helps if you bring up a panel with
a throttle gauge on it on the screen so you can see where your throttle
setting actually is. That makes it quite flyable. I've landed
everything from Cessnas to F-18s to 747s well using a gamepad.