Instead of using marled yarn, or holding two strands together, why not K1 in color 1, then K1 in color 2, then 1, then 2 and so forth, to make the marls really look woven? You might be able to get by with fewer butterflies that way.
I've never liked marled yarn, and the marls I've seen in tartan/Argyle hose don't look very nice, I don't think.