Is there any way of avoiding the external module and catch an arbitrary number of nested parentheses with a "normal" Regex? I know that the Owl book says it can't be done, but I would like to put my mind at rest on this issue.

It depends on what you call a "normal" regex. If normal means without any perl specific things, it can not be done. But if you don't mind a perl specific regex, perlre has the solution:

The following pattern matches a parenthesized group:

$re = qr{
          \(
          (?:
            (?> [^()]+ )    # Non-parens without backtracking
           |
            (??{ $re })     # Group with matching parens
          )*
          \)
        }x;

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2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
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