If you do not have the 13 Arduino pins available, PISO shift registers were invented for your problem. Forget about the analog trick in your case.
µC is about serializing the physical world to handle it in a sequential processor 
If you do not have the 13 Arduino pins available, PISO shift registers were invented for your problem. Forget about the analog trick in your case.
µC is about serializing the physical world to handle it in a sequential processor