Since you're using the v3 API you could simply prevent the infoWindow from shifting the map with the disableAutoPan option.
Complete example: 
<!DOCTYPE html>
<html> 
<head> 
   <meta http-equiv="content-type" content="text/html; charset=UTF-8"/> 
   <title>Google Maps disableAutoPan Demo</title> 
   <script src="http://maps.google.com/maps/api/js?sensor=false" 
           type="text/javascript"></script> 
</head> 
<body> 
   <div id="map" style="width: 200px; height: 200px"></div> 
   <script type="text/javascript"> 
   var myLatlng = new google.maps.LatLng(37.44, -122.14);
   var myOptions = {
      zoom: 4,
      center: myLatlng,
      mapTypeId: google.maps.MapTypeId.ROADMAP
   }
   var map = new google.maps.Map(document.getElementById("map"), myOptions);
   var infowindow = new google.maps.InfoWindow({
      content: 'Test',
      disableAutoPan: true
   });
   var marker = new google.maps.Marker({
      position: myLatlng,
      map: map,
      title: 'Test Marker'
   });
   google.maps.event.addListener(marker, 'click', function() {
     infowindow.open(map, marker);
   });
   </script> 
</body> 
</html>
Screenshot:

There is no equivalent to the disableAutoPan in the v2 API's GInfoWindowOptions, and I am not aware of any workarounds for this.