Only way I know is to edit the xml manually, if you open in notepad then Ctrl and F then in the search box type AxisKeys0 that will find the entry for X++ if you want x-- then its AxisKeys1, Y++ its AxisKeys2 etc etc.
The other way to do it is to click on the hotkey to open the keystroke entry box and then just pres the red cross, that should enter zero in there which I think will basically be ok as well.
Hood