Sorry, I've never used google maps as an imagery source. (I've only used data sets that already include the georeference information embedded in them - ie GeoTIFF or JPEG2000) in many of our WED projects. A user named "Snow" made a post a while ago on the org, which showed (a somewhat convoluted) method for obtaining the LAT/LONG coordinates for Google imagery - however it was a laborious manual process to do each tile. You may want to instead use something like the Gmaps or G2XPL utility to download images for you on an area, then import the resultant DSF back into WED. Not ideal, but may point you in the right direction.