Multiple Inheritance Concern

Hello PHPers, I've learned that php doesn't support multiple inheritance, b/c if you need multiple inheritance usually it is a sign you've got a design imperfection...or so they say. Well, I'm using a framework (Codeigniter), and i'm extending the core libraries. The trouble is, I want to also extend a second custom class, and I don't want to change the core codeigniter class definitions as this makes for awkward upgrades. I read about mixins - no thank you. i do not want to even think about mixins as it looks like it would be the source of all debug hell... What's a programmer to do? Is the only option i am really left with to duplicate the code in each class? Thanks, dK `