I had to go searching for the answer to this but I knew it was there somewhere. (Ancient Discussion) It came up about halfway down the page and the final answer is at the bottom. Sorry, abilities added through Arcane Bond cost full price. But, unlike someone who is upgrading an item, the wizard doesn't have to give up their item to have it done.
[sblock=OOC]Ah, makes sense. In that case, he'll drop the Page of Liberating Command and spend the combined funds on upgrading the dagger.[/sblock]