Hello Guest! Did you know that ProjectKorra has an official Discord server? A lot of discussion about the official server, development process, and community discussion happens over there. Feel free to join now by clicking the link below.
That would need to be done through a chat plugin, which would probably interfere with the plugin's prefixes. You could try turning back on your chat plugins, and using a custom bending choose command made through something like CommandHelper that would choose their bending for them and set their prefix, while overriding that with your staff prefixes. For example, you could set up a command alias like "/firebender" that would run "/bending choose fire" for the player, and also run the commands to set their prefix to fire.