[self-modifying code.]

    Also, I was thinking more along the lines of the lookup table
    being in RAM, not compiled in. So you just modify the RAM table
    for different duty cycles - although that would take a few cycles.

Right.  They're very similar.  I was thinking along the lines of:

        for (i=0; i < 256; i++) {
            PWMCODE[i] = asm("NOP");    /* More fictional syntax! */
        }
        for (i=0; i < 8; i++) {
            PWMCODE[stoptime[i]] = asm("BCF port, i");
        }
        PWMCODE[256] = asm("ret");
        while (1) {
            outp(port, 255);            /* All bits on */
            asm ("call PWMCODE");       /* Call code to turn them off */
                                        /*    at appropriate times */
        }

This saves you one instruction (50%!!!) (assuming a pic) for each time you
only need to change one bit on the port, because you can put the bit number
in a single instruction instead of having to load w and then output it.

BillW