This fails for me with multiple escaped " inside string. For example:

my $str = <<'EOS';
"\"$x\""
EOS
$str =~ s[("[^"]*?(?<!\\)")] 
         {
             (my $temp = $1) =~ s[(?<!\\)\$][\Q\$]g;
             $temp;
         }mge;
print $str;
[download]

does not escape the $.