sudo niutil -createprop . /users/shortname home \Replace shortname with the user's shortname, and you should be done.
/Library/WebServer/Documents/shortname
[Editor's note: I added the backslash to narrow the displayed command's width. If you enter this as one line, you do NOT need the backslash! Note that I haven't test this hint myself, but it should work as described based on niload's man page.]

