I hope this makes sense:

Is there a any way to display a message text on a conversation window without the other person(s) in the conversation seeing it? I need this feature for a plugin that would notify the user (only) thru the conversation window.

The handwriting plugin has feature like this - when the reciepient does not support handwritten messages it would notify the user of this.

I need to do something like this.  Does the Messenger Plus! API have support for this directly?

Thanks in advance..

i don't think its possible and the handwriting plugin doesn't do it, as it just enables such features already built into Messenger