Using the Google Static Maps API with a Grid Layer.
A Grid layer with a custom getURL method can be
used to request static maps for a specific extent and zoom
level. The Google Static Maps API is the most reliable way to
get Google base maps in OpenLayers. Note, however, that the
free version of this is limited to a map size of 640x640 pixels
(1280x1280 if the scale=2 url parameter is used)
and 1000 page views per viewer per day. Every map center
or zoom level change increases the page view counter by 1.
Look at the google-static.js source to see how this is done. See the Static Maps API V2 Developer Guide for details on the API.