"So IBM's guidance guidance that will not go down well with users."
Uh... why not?
patch and boot the secondary, patch and boot the primary. Extra points if you are nice enough to disable the vscsi and vfcs of the corresponding vios first (rmdev -pl $adaptername). Ethernet fails over automatically, though you could add extra grace there as well.
Hardly a big deal. And in order to run into iv91339s bug, you´d have to have a failing lpm in first place.