As mentioned in your referenced node on "How do I get a reference to a builtin function?", you cant.

Here are alternatives:

Wrap the function:

>perl -e "my %f=(chr=>sub{chr(shift)});  print $f{$ARGV[0]}->($ARGV[1]
+)" chr 35
#
>perl -e "my %f=(chr=>sub{chr(shift)});  print $f{$ARGV[0]}->($ARGV[1]
+)" chr 36
$
[download]

Use eval (more general, but potentially unsafe):

>perl -e "print eval qq|@ARGV|" sqrt 2
1.4142135623731
>perl -e "print eval qq|@ARGV|" chr 128
Ç
[download]