You need an additional window for that, meaning something around the lines dubealex did in his AMS long, long ago... so if you're using RMXP, this'll be the script for you.
If you wanna do it by yourself or use RMVX, here's what you wanna do, roughly outlined: Create a new window, let it be called from the message window's definitions (you might wanna trigger it by asking for a name given in the message string itself) and show it when it's != nil or whenever you want to show it. If you need further assistance with that, feel free to ask.