If the Nameless One is not part of the Xaositect faction, there is no way to avoid a fight with Tiresias. With 13+ Dexterity, TNO can snap his neck before he calls for reinforcements, otherwise, a full blown fight will break out.
If TNO is part of the faction, he can be bribed to give information about the area.
Sybil can also be turned in to him (no experience, just an alignment change).
With Qwinn's Fixpack, the only way to learn about the shortcut to the Tenement exit is to convince Tiresias to give that information (only if TNO is a member of the Xaositects), making him a more useful character overall.