c:\@Work\Perl\monks>perl -MO=Deparse,-p -i -lpe "s/^\s*$/<r><\/r>/g"
BEGIN { $^I = ""; }
BEGIN { $/ = "\n"; $\ = "\n"; }
LINE: while (defined(($_ = <ARGV>))) {
    chomp($_);
    s[^\s*$][<r></r>]g;
}
continue {
    print($_);
}
-e syntax OK