From your badge, you have an IS Boxer/Inner Space subscription.

Why not make a mapped key, for Tremor Totem.
Give it the hotkey: S, since you're already used to that.
Either:
a) Have one step for each Shaman, which sends the "S" key to that Shaman only... and likely set the mapped key to not advance to the next step for half a second or so, to protect you against accidentally spamming the key; or
b) Put each of your Shammies in the same Action Target Group, and use that ATG as the target for the single step on the Mapped Key... just check the box to round-robin, within the target group... probably do the same, do not advance for at least 0.5 seconds...