Aspect Oriented Programming is not very widespread in the PHP world yet. I'm not sure CI has any facility for this. Your best bet is likely to google AOP PHP to find an implementation.
Some libraries (including dead ones)
- https://github.com/goaop/framework
- http://code.google.com/p/phpaspect/
- http://www.aophp.net
- http://www.seasar.org/en/php5/index.html
- http://php-aop.googlecode.com
- http://flow3.typo3.org (as part of their full stack)
- https://github.com/AOP-PHP/AOP