(Update: I hadn't seen your follow-up note about the -d:NYTProf before posting this... If you need to do it from within the Perl code itself, this of course wouldn't work.)

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You could use the respective system call tracing tool, e.g. on Linux:

$ strace -e execve -s 200 perl -le '$/ = "\0"; open my $fh, "/proc/$$/
+cmdline"; print for <$fh>'
execve("/usr/local/bin/perl", ["perl", "-le", "$/ = \"\\0\"; open my $
+fh, \"/proc/$$/cmdline\"; print for <$fh>"], [/* 71 vars */]) = 0
[download]

(add the option -f in a more complex setup, where perl is being called somewhere further down the fork-exec line...)

Other systems have other system call tracers  (see this node for an attempt of mine to put together a list).

This approach isn't really portable either... but you should at least be able to get it working somehow — which you otherwise couldn't if there's no /proc file system.