This topic is a good one. Our merit sources have been up and doing but just as the OP rightly said, most times they can be too busy to run through all the threads to find all the Merit deserving posts. Recently one of our own @1miau ran such thread which is already closed.
https://bitcointalk.org/index.php?topic=5544411.msg65416874#msg65416874
I also noticed how he was able to distribute merits among almost every post which was shared there.

Even though it was a good idea, he also noted how users were going against the rules of not posting more than once in a month there. There are more merit farmers now than good post seekers currently but I think the final decision would be left for the merit sources and moderators to decide.

On the contrary, I would suggest they share the threads among themselves where each of them would concentrate more with his merits so that they can be able to cover more threads than 3 or more of them concentrating in one threads while other threads remain untouched.