It's not really that hard, when you look at the rein reports most of the names are quickly identifiable as your allies. While there may be a few hundred rein reports each day, its just the same people sending reins every day.
Of course it is also often the same people sending "joke" reins every day, which makes it fairly easy to find them and send them home.
It's a worthwhile activity, not just to get rid of the offense, but you'll also find opponents who send 100 phalanx. Those are there to get "scout reports" on your defense. You can look at the percentage of troops lost for a Natar attack to get a rough estimate of how much defense is in each of your opponents wonders (I've also landed my hero 1 min before a natar attack on an opponents wonder to do the same thing).
And while reading the RP is a pain, there are parsers available that you can paste a copy of your RP into that make it much faster.