I probably shouldn't post this one because it's obscure enough that I can't find a dictionary with an etymology. I can tell you my guess -- which is that it's another colorful 19th century Americanism -- but that's just a guess (if anyone has access to an OED, I'd appreciate checking for this one). But in the end, it just sounds too good to pass up posting it. I suspect the second A can also be pronounced long, but the one time I've heard it, the person used a short A, roughly that of "cat". Besides, have a personal use:
Because I've been lazy, the dirty dishes are cancatervated in the sink.