I would try to find a different role for your colleague where he performs better (e.g. tech support, creating mockups, gathering user feedback). The CEO doesn't

I would try to find a different role for your colleague where he performs better (e.g. tech support, creating mockups, gathering user feedback). The CEO doesn't need to directly assign him to this new role but rather give him more and more tasks and responsibilities in this area. Also you should try to negotiate more equity with the CEO.