I'm afraid the entire draw order is keyed together. Spine doesn't know which part of the draw order (which is a list of slots) is important to you, so it can't mix two draw orders.
You could achieve your goal by using attachment visibility keys. For example, you could duplicate a slot so it is in the draw order twice, but only show an attachment for one of the two slots at any given time.
CobraCommander Your new forum redesign doesn't allow me to attach screenshots, by the way.
Yep, we'll be adding attachments soon! We wanted to get the new forum up ASAP, so it only has the basics.
Thanks, we've fixed them up now!