I decided that I better work both sleeves of the Wash Sweater at once. That way, if I stall out again, I won't have to figure out how to make the second sleeve match the first: each decision I make I will make for both sleeves simultaneously so they'll match without any extra pain and effort.
I also decided to work from the inside and outside of a center-pull ball, so that the inconsistent dye jobs on the yarn will at least match sleeve to sleeve. But my yarn was tangling. After a couple attempts to mangle a wire hanger into shape, I came up with this:
Something heavier would probably work better to keep the whole thing place, but this does seem to be doing the job: the ball doesn't flip around, and I can keep the strands from winding around each other.