A basic WordPress controller

gistfile1.php

<?php
define( 'DB_VH_REWRITE_TAG', 'feed-relay' );


add_action( 'init', 'db_vh_create_feeds_relay_urls' );

function db_vh_create_feeds_relay_urls() {
  add_rewrite_rule(
		$rule = 'feeds/(.*)/?',
		$rewrite = 'index.php?' . DB_VH_REWRITE_TAG . '=$matches[1]',
		$position = 'top'
	);
	add_rewrite_tag( '%' . DB_VH_REWRITE_TAG . '%', '([^&]+)' );
}

add_action( 'wp', 'db_vh_feed_relay_controller' );

function db_vh_feed_relay_controller() {
	global $wp_query;
	if ( isset(
		$wp_query->query_vars[ DB_VH_REWRITE_TAG ]
	) ) {
		$requested_feed = $wp_query->query_vars[ DB_VH_REWRITE_TAG ];
		// Do something. Probably a switch on $requested_feed.
  	}
}