I can think of a couple of directions you might choose to take your students without focusing on reading. First, you might show them how to make up their own chord charts for songs that have their lyrics posted on line, and how to transpose those songs into keys that are most useful to them. This can go along way towards allowing the student to study the kind of music they are interested in. Second, you might choose to open the door to melodic patterns and sequences study, which can take a considerable period of time to cover completely and may inspire you and your students to learn at least basic sight reading. From this point, you may find one thing leads to another and the learning never really has to end.