There's a discussion of this elsewhere, in the bigdisk builder thread. It can be done, but it then forever requires a Hijack kernel to keep it that way, and one must never again even attempt to apply a factory .upgrade file.

Because the initrd in flash is where the partitioner resides, and ISTR that it attempts to "correct" the partition table on every boot (or is that on every .upgrade?.. don't rememeber).

I've hacked Hijack to intercept and prevent this "correction", but I don't remember whether that change went into the main release, or was just played with out-of-stream.

Cheers