Why don't you create a script to run from the crontab to do it for you on a regular basis, say once a week/month? That way you could have a bit better control as well, and perhaps even introduce some date-stamping of the backup files as well, plus deleting them after a set time period.
Example script below , line 1 and 4 isn't correct, but it will give you an idea how to do it.
DATE=`date %dd%mm%yy` (do a man date to see the correct fmt)
cp /var/log/syslog /var/log/syslog$DATE
>/var/log/syslog
find /var/log/syslog* -mtime 30 exec rm{}; (do a man find)
Hope this will help you
Chris IBM Certified Specialist - MQSeries