If the text is in a TextField (and is not just a text object), the approach above works, by setting objectPath.presence="visible" for the mouseEnter event for the TextField, and by setting objectPath.presence="invisible" for the mouseExit event for the TextField.
Also, if you want there not to be a blank space where then the item is invisible, set it to be "hidden" instead, and set the layout of the page to be flowable.
Sarah