I chose to look for empty spells. There aren't alot of them, but my locks have fear, deathcoil and howl of terror to round-robin, so I chose to mess with them first.
I picked curses. They are pretty cheap, like 400 mana, work on enemies and pretty much always go through (no facing requirements). So I stuck in a curse every blank spot.

/castsequence [@focus-target] reset=100 Curse of the Elements, Death Coil,

/castsequence [@focus-target] reset=100 Curse of Tongues, Curse of Tongues, Curse of Tongues, Death Coil,

The problem is the spell needs to be castable on enemies or the castsequence gets pisses that you put a spell you can cast on your self in with a spell you want to cast on an enemy. So when I picked blood pressence for my DKs, since it is cheap (no rune) and simple (only GCD), it fails since I can't be cast on an enemy.
(Does Not Work)
/castsequence [@focus-target] reset=100 Blood Pressence, Rune Tap,

I am stil looking for my DKs. I hope to find it, 5 Rune Taps is too much, so I like to use 1, 2, 2. I glyph it ito work across everyone in the group.

I wish you luck into finding a round-robin replacement for commas. I could do it in my key-broadcasting software, but I don't always put the round-robin spells on the exact same keys. I don't want to have to worry about doing something out of game, that can be done in game (if Blizzard ever gets pissed if I am doing something they don't want to get around something they took out). And it makes it changeable. Maybe the new playstyle is to have all 5 lock deathcoils for a big punch instead of worrying about the mini-fears.

Hope that helps and good luck.