Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 19736)
+++ wp-includes/user.php	(working copy)
@@ -977,7 +977,11 @@
  *
  * @since 2.3.0
  * @uses $wpdb WordPress database object for queries
- *
+ * 
+ * @uses apply_filters() Calls 'wp_dropdown_users_pre' with first parameter false and second
+ *   value $args
+ * @uses apply_filters() Calls 'wp_dropdown_users' with first parameter set to $output
+ * 
  * @param string|array $args Optional. Override defaults.
  * @return string|null Null on display. String of HTML content on retrieve.
  */
@@ -992,6 +996,10 @@
 	);
 
 	$defaults['selected'] = is_author() ? get_query_var( 'author' ) : 0;
+	
+	//allow plugins to override user dropdown before any queries are made
+	if ( $out = apply_filters( 'wp_dropdown_users_pre', false, $args ) )
+		return $out;
 
 	$r = wp_parse_args( $args, $defaults );
 	extract( $r, EXTR_SKIP );