How to delete specific controls from an input device?

I use several input devices, amongst other I have 2 Joysticks.

On one joystick I just want to use the slider, all other buttons and axes should be switched off. But as soon as I change a control, I have to select a control. I can do a "Clear current input" but then I have to select another one, press a button or move an axis.

On that specific joystick the sim made some default assignments. I want to get rid of them.

Thx,

Karl