I think you want the "/s" switch to the screensaver program.
This works for me, for example (if I'm in the screensaver directory):
my $scr = "sspipes.scr";
Update: Trying it with a random screensaver works too, so it seems /s is the correct, general solution. Again (lazily) from within the screensaver directory:
my @ss = glob("*.scr");
my $scr = $ss[rand @ss];
substr+lc crypt(qw $i3 SI$),4,5