I believe you mean Larzuk?
And yes, his quest is the only way to add sockets to a unique item.
One can however upgrade a unique item’s quality in the cube. For example, upgrading Biggin’s Bonnet from a cap to a war hat, or Vampire’s Gaze from a grim helm to a bone visage.
There is a list of useful cube recipes here:
http://classic.battle.net/diablo2exp/items/cube.shtml