My thought: sis "to express contempt" (Chambers) - one meaning of "poll" is "the head" (Chambers). A = alpha, eg alpha dog, alpha male, which could be taken as the head. Gives one "sisa". Support can mean "back up" (Chambers again), so, sisa backwards gives asis. Phew!
I wasn't too happy with the 'express' element myself, but I'm not sure why one should go for sis in the absence of any reference to contempt or South Africa.
One can express all sorts of things including milk from a nipple, pus from a wound...as well as sadness, joy and a host of other emotions. Just seems extremely thin to me, but you may well be right, Stultus.