Hide overlay under area

I am trying to find a way of hiding just the left half or just the
right half of a GTileLayerOverlay. (The user will choose which side
with a checkbox, but that isn't important).

My first thought was to create two GLatLngBounds variables, one for
the left half of the map and one for the right half. Called, leftbox
and rightbox.

What I now need is code that does something like;

if (checkbox for leftbox = true) {hide all the tiles for
GTileOverlayName that are underneath leftbox} else {do nothing);

Any ideas how this could be achieved? The checkbox part/if statement
isn't a problem. But how can I selectively hide parts of a
GTileLayerOverlay, based on GLatLngBounds

Thanks