YOU COULD START BY SAYING

 - "That is a good topic".

-  " I like that topic".

- "I have a better topic. Let me tell you about..."

- "I could talk about that forever."

- "I cannot easily talk about that topic".

- "Let me tell you about something else".

 - "I have thought about this Topic a long time." 

- "I can tell you what you ought to know."

- "I remember only parts of that Topic."

- "You ought to call, so we can talk about this one."