(PECL memcached >= 0.1.0)
Memcached::addByKey — Add an item under a new key on a specific server
$server_key
   , string $key
   , mixed $value
   [, int $expiration
  ] )
   Memcached::addByKey() is functionally equivalent to
   Memcached::add(), except that the free-form
   server_key can be used to map the
   key to a specific server. This is useful if you need
   to keep a bunch of related keys on a certain server.
  
server_keyThe key identifying the server to store the value on.
keyThe key under which to store the value.
valueThe value to store.
expirationThe expiration time, defaults to 0. See Expiration Times for more info.
   Returns TRUE on success or FALSE on failure.
   The Memcached::getResultCode() will return
   Memcached::RES_NOTSTORED if the key already exists.