Some years ago I made a small project using 12 LED powered on 4 pin on a PIC.
Now I'm making a bigger library for Arduino in order to contol, using N pin and POV, Nx(N-1) LED. I made a 90 led pannel (15x6) driven by 10 pin. Excepting for N resistors and N diodes, no extra hardware is required.
Now I'll try to make a 3 wire interface and test this library. I'll put here a link when finished.
Not yet finished... here Control de N2 -N leds usando N pin (+ interfaz 3 hilos en progreso) - Proyectos - Arduino Forum