Changing pwdlastset attribute

I have a script that resets the pwdlastset attribute to the current date.  I have a couple of questions.

1.)  Is it possible to set pwdlastset to a random time within a set period.  Example would be the timestamp could be from Aug. 2013 to Sept 2013?

2.) If is the above is possible.  How would you script based on a last name to randomize the timestamp?    Example last name A - M Aug. 2013 to Sept 2013 timestamp, N - Z Oct. 2013 to Nov. 2013 timestamp.

Thanks