Switching on/off 5V power to a USB port

I just got a little USB powered fan and it sure would be nice if I could 
have cron on my FreeBSD box turn it on or off at certain times by 
switching off the 5V line on a USB port.  Anyone know how I can do 
that?  Thanks.

BTW this is a pretty decent fan for the money. :)  
http://www.amazon.com/gp/product/B0033WSDOM/

-- 
Ron McDowell
San Antonio TX