Open Software License attribution notice

[opensource.org at alias001.spaceandtime.org]

Suppose I want to force the authors to be retained as well as the
copyright holder.  So let's say Joe Schmoe works for Dumb Corporation
and they agree to release under the OSL.  Here is my file (please
correct me if it should appear differently):

------------------------------
test.c
Copyright (C) Dumb Corporation
Licensed under the Open Software License version 2.1

Original version: Joe Schmoe 2004-08-18

int main (void)
{
   return 0;
}
------------------------------

Is "Original version: Joe Schmoe 2004-08-18" part of the "Attribution
Notice".  I'm assuming it's not.  How can we make a list of the authors
(that work for Dumb Corporation) part of the Attribution Notice so that
licensees can't remove it (just like the copyright notice).

Thanks.