Before the automatic "move discussion to chat" link appears, or when it appears? — Daniel Fischer ♦ 11 hours ago

Before it appears - I am trying to be a good guy! — Rob Arthan 11 hours ago

Then I think you need to create a chatroom for you and that user yourself - the other user needs 20 network reputation, or they won't be able to participate - and invite them. That doesn't copy the comments you two made so far to the chatroom, however, like the automated thing does. Waiting for the system to suggest chat has its upsides. — Daniel Fischer ♦ 11 hours ago

Of course, you can also copy the comments manually one by one. It might be useful to provide also some context to the conversation; in case someone gets to the room not from the particular question. (You get link to a comment simply by clicking on the timestamp.) For example like here: chat.stackexchange.com/transcript/message/19743313#19743313 — Martin Sleziak 30 secs ago