With Keyclone, that's about the only option I can think of.

You can do Keymaps/Hotstrings, where you press one button and it sends another.
But effectively, that is the same thing.

You can Blacklist or Whitelist, but that is for all clients.
So the easiest is to have a Keybind (within wow) for whatever toon, but to not have that on the others.

I know the the InnerSpace Keymaps, you can have keys go to one client but not the others.
You can go by Slot (account), Toon Name, Predefined group, All without current window and All with current window.
To my knowledge there's nothing like that in Keyclone.