If your trying to escape the embedded quotes before passing it to Text::CSV, then this might do the trick.

Note: I've added some extra embedded quotes to check that it doesn't escaped already escaped quotes and handles the edge cases at either end of the string. You'll need to throw a few more tests at this before using it in anger.

$s='"crosby","stills","nash",""and" ""sometimes"" "young""'

# capture everything between a quote and a quote 
# follow by a comma or the end of string
 $s =~ s[ " (.*?) " ( , | $ ) ]
 { 
     # Look for unescaped embedded quotes and escape them
     (my $t = $1) =~ s[ (?<!") " (?!") ][""]gx; 
     
     # put back the outer quotes and the comma if there was one
     '"' . $t . '"' . ($2||''); 
 }gex;

print $s;
"crosby","stills","nash","""and"" ""sometimes"" ""young"""
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This assumes that $s would otherwise be parsed correctly by Text::CSV.