I heard that even things other than Udi could have healing power if linked to Baba. Is there a story about this in the text?

Yes, Chapter 33 recounts a remarkable incident involving a friend of Narayanrao who was stung by a scorpion. In his friend's moment of severe agony, Narayanrao could not find any of Baba's Udi. Desperate, he prayed to a picture of Sai Baba and noticed the ash from burnt incense sticks at the bottom of the frame. The text states he considered this ash as Udi, and upon applying a pinch of it to the sting while chanting Sai's name, the pain subsided immediately. This story beautifully illustrates that the faith and feeling behind the application were paramount, as the incense ash, when considered as Udi, manifested the same miraculous healing power.