This isn't a Perl solution, but I'd just hook some custom elisp functions up to cperl-mode for this. The advantage of this approach is that the functions can look at the syntax information in the text properties, so that you can for example choose not to alter the whitespace inside strings or comments, without writing any code to parse where strings and comments begin or end -- one less wheel to reinvent. The disadvantage is that you have to know elisp, in addition to Perl.