I really like the idea, I was actually going to suggest this feature the other day.
Another feature I was going to suggest was a Personal Message tag, because at the moment, we have:
- (!MP) - Your Own Email
- (!M) - The person you're talking to's email
- (!N) - The person you're talking to's screen name
- (!CN) - The person you're talking to's custom name
Would it really hurt to have (!PM), which would be their personal message?