I think that generally disabling SysRq while xscreensaver is running is not a good idea. It will prevent the use of other commands that might be useful if the system is behaving troublesome.
I think that a setuid helper specifically for this task is the proper solution, if it can be ensured that it can only be used for xscreensaver processes. -- To UNSUBSCRIBE, email to debian-bugs-rc-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org