I like the "cut of your jib" Minstrel! Sounds like a very likely hypothesis to me. But like the other posters, I have only seen/heard/understood it as a reference to being "not made to measure" from the clothing industry and always understood it to have originated from there. At least, that's what me dad told me when I was a lad :-).
I think it could have easily have worked the other way however. Its not hard to imagine a sailor, home for a few days, visiting the dockside tailors shop for a new suit, being offered one "made to measure" but because he was away again soon, asking for one "off the peg" (if minstrels idea of the phrases shipboard usage is correct) because he was in a hurry. Its easy to see how the term could have crossed over, especially in the ports.