First off, look into using the automysqlbackup.sh script (
http://sourceforge.net/projects/automysqlbackup/). That will make backup simpler. Then just call the script from the dumppreusercmd.
$sshPath -q -x -l backuppc $host /usr/bin/sudo /path/to/automysqlbackup.sh
Of course with the example above you'll have to add a line to sudoers such as:
backuppc ALL=NOPASSWD: /path/to/automysqlbackup.sh
Ryan Manikowski