I've created a custom macro that gets and parses session value with the latitude and longitude the user has searched for and auto populates the default latitude and longitude. Only customization I had to do to the webpart was in the DataSourceControl_OnFilterChanged event, I set

BasicGoogleMaps.MapProperties.Latitude = this.Latitude;
BasicGoogleMaps.MapProperties.Longitude = this.Longitude;

because the session value was set in the OnPreRender event of the filter control and when I called RaiseOnFilterChanged(), it updates the filter and triggers the map webpart to update. Worked slick!