Paul, someone pointed this post out to me, and I wanted to add a comment to clarify, but yes, you can do unbalanced Publisher machines in 12.10 and later as well. Here is the link to the Help on how to do things, it is pretty much the same for both tracks:
Hopefully this is what you needed and will hopefully help others that find this post. It is a little complex, but if you play around with things it should make sense pretty quickly. Oh, just a side note, there will be an update to the QVS unbalanced clustering help shortly, we noticed some missing info, so that is being added, I would venture it should be posted in the coming weeks from the date of this post, it will have instructions on how to do the config changes if you are running IIS as the web server as well now.