As you mention, I think the issue with "winging it" (sorry) on the stands is the possibility of introducing twist along the way.
An alternative to the plans-specified floor-to-ceiling setup that a lot of builders have done is a set of floor-mounted towers. This is what I used - in fact I got them for free from another builder - but in my case, I was building my wings in a rental house and so instead of mounting the stands to the concrete, I built 2x6 frames for them. I made the frames with adjustable "feet" so I could level and square the stands themselves prior to introducing the wing skeletons.
You can see/read a bit about my wing stand construction here: http://rv.squawk1200.net/2014/06/30/...-organization/