@flannan He's a giant Leviathan, so I doubt he'd find anyone he'd consider making a contract with very easily, and most would be too scared to even try and talk to him.
Also, maybe the name is contract-specific, so that he knows who is calling based on what name they use? I don't know how it's intended, but the way it was worded made me think that might be how it works. Or, a "temporary contract" could also mean that the name used is also temporary, as in the name loses its meaning when the contract expires.