@Cage,

I wonder what would happen if you used separate headers in one pz2 file, something like this?

{
version
    {
    number 8
    }
actor hip:1
    {
    channels
        {
        targetGeom R_spread
            {
            [channel contents]
            }
        }
    }
}
{
version
    {
    number 8
    }
actor hip:1
    {
    channels
        {
        targetGeom R_spread2b
            {
            [channel contents]
            }
        }
    }
}

It's only a guess, but may be worth a try. Poser might parse this as separate pose files, and thus allow more that one morph to be loaded from the same file.