Depending on the version you are running, just put the command (younameit) into the Macro line (I'm looking at 2010).
So, for 2010 for example: C^C^_younameit
Be sure the routine Ron provided is in a directory that AutoCAD looks at.
In the older versions there is an <MNS ??> file you would need to edit. I don't recall the layout so I can't post an example here for you, but I know it's somewhat similar.