You're not the first person to want to do this. I made this change in the trunk a while ago at the request of another user. You can check out the source from subversion and build a new jar. See the gwt-google-apis Maps FAQ (
http://code.google.com/p/gwt-google-apis/) for some details if you are unsure how to do this.
Keep in mind that we are working toward a release candidate right now and are pushing through some API changes in some types to use JavaScript overlays which change the way you construct new instances for many types (use static factory method newInstance() instead of the new operator.)