I use this jQuery code to set the mouse pointer to its busy state (hourglass) during an Ajax call...
$(\'body\').css(\'cursor\', \'wait\');
I haven't tried this, but what about if you create a transparent div that is absolutely positioned and fills the viewport just before changing the CSS. Then, when the css is changed on the body, remove the div. This might trigger a mouseover event on the body, which might cause the cursor to update to the latest CSS value.
Again, I haven't tested this, but it's worth a shot.