Implement a hack so swill can twiddle the marker manager ;)

gmap.module

@@ -246,6 +246,11 @@ function _gmap_doheader() {
   drupal_add_css($gmap_path .'/gmap.css');
   drupal_add_js($gmap_path .'/js/gmap.js');
   $mm = variable_get('gmap_mm_type', 'gmap');
+  // If you really really want to override the marker manager, implement
+  // this, take $mm by ref, and have fun. --Bdragon
+  if (function_exists('_gmap_markermanager_override')) {
+    _gmap_markermanager_override($mm);
+  }
   if ($mm=='clusterer') {
     drupal_add_js($gmap_path .'/js/icon.js');
     drupal_add_js($gmap_path .'/thirdparty/Clusterer2.js');