In your message box, use /n[x], where x is the hero's ID number. So the first character would be /n[1], the second would be /n[2], etc.

So "Hello /n[1]" might show up in-game as "Hello Cube". Just remember that you need
to leave room on the line for the character's name - just because /n[2] fits on the end of a line, doesn't mean that SuperArmorGuy will.

(Basically, it works the same way as /v[x] works for variables and /c[x] works for colors)