I\'ve found this answer which look like what I need:
How can I programmatically generate keypress events in C#?
Except for the fact I can\'t create an insta
phewwww
I've found it: Keyboard.PrimaryDevice.ActiveSource has to be used
Keyboard.PrimaryDevice.ActiveSource
InputManager.Current.ProcessInput( new KeyEventArgs(Keyboard.PrimaryDevice, Keyboard.PrimaryDevice.ActiveSource, 0, Key.Tab) { RoutedEvent = Keyboard.KeyDownEvent } );