I saw this sort of scheme yesterday, as I said.  The "trickery" that was used was simply only turning on one LED at a time.
In the example I've seen, this is how it's done

----+ +----------------------------------------+
    | | +------------------------------+       |
    | | | +--------------------+       |       |
    | | | | +----------+       |       |       |
    | | | | |          |       |       |       |
    | | | | |          \       \       \       \
    | | | | |          /       /       /       /
    | | | | |          \       \       \       \
    | | | | |          /       /       /       /
    | | | | |          \       \       \       \
    | | | | |          |       |       |       |
    | | | | |          |   +---+   +---+   +---+
MCU | | | | |          |   |   |   |   |   |   |
    | | | | |          |  ___  |  ___  |  ___  |
    | | | | |          |  \ /  |  \ /  |  \ /  |
    | | | | |          |  ---  |  ---  |  ---  |
    | | | | |          |   |   |   |   |   |   |
Pin1|-------+--------------+-------+-------+----
    | | | |            |       |       |       |
    | | | |        +---+       |   +---+   +---+
    | | | |        |   |       |   |   |   |   |
    | | | |       ___  |       |  ___  |  ___  |
    | | | |       \ /  |       |  \ /  |  \ /  |
    | | | |       ---  |       |  ---  |  ---  |
    | | | |        |   |       |   |   |   |   |
Pin2|-----+--------+---------------+-------+----
    | | |              |       |       |       |
    | | |          +---+   +---+       |   +---+
    | | |          |   |   |   |       |   |   |
    | | |         ___  |  ___  |       |  ___  |
    | | |         \ /  |  \ /  |       |  \ /  |
    | | |         ---  |  ---  |       |  ---  |
    | | |          |   |   |   |       |   |   |
Pin3|---+----------+-------+---------------+----
    | |                |       |       |       |
    | |            +---+   +---+   +---+       |
    | |            |   |   |   |   |   |       |
    | |           ___  |  ___  |  ___  |       |
    | |           \ /  |  \ /  |  \ /  |       |
    | |           ---  |  ---  |  ---  |       |
    | |            |   |   |   |   |   |       |
Pin4|-+------------+-------+-------+------------


----- Original Message -----
From: Wouter van Ooijen <wouter@VOTI.NL>
Date: Thursday, June 10, 2004 9:31 pm
Subject: Re: N*(N-1) LEDs on N pins
>
> I multiplex by N-1 LEDs. Some trickery is needed because the current
> through the 'on' LEDs depends on the number of on LEDs.
>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
> consultancy, development, PICmicro products
>
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