Disable a button on a iPhone toolbar

Hello,

buttons are created like this :

left = Titanium.UI.createButton({
    image:'../images/icon_arrow_left.png'
});
 
right = Titanium.UI.createButton({
    image:'../images/icon_arrow_right.png'
});
 
var flexSpace = Titanium.UI.createButton({
    systemButton:Titanium.UI.iPhone.SystemButton.FLEXIBLE_SPACE
});
win.setToolbar([flexSpace,left,flexSpace,right,flexSpace]);

Regards