As everyone else has pretty much stated, you just can’t simply remove paste. People can macro type, use alternative chat clients, and more. There will always be a way to dump text into a chat. What you seem to need is better moderators. If you want r9kbeta on, turn it on and remove the moderators who keep shutting it off.
You can have a bot that auto bans/times out the common copy/paste spam; turn on r9k mode. That should handle the majority of spam problems. You could write an autoban for special characters in general. (Non standard ASCII)
Some more on R9KBeta
This command will not allow users to post non-unique messages to the channel. It will check for a minimum of 9 characters that are not symbol unicode characters.
Usage: /r9kbeta
Note: R9K is a unique way of moderating essentially allowing you to stop generic copy-pasted messages intended as spam among over generally annoying content. To find out more about what R9K is we highly suggest reading this blog post.