What length are your circulars? If they're shorter - 16" - you won't need to divide them. If they're longer than that, you can do the half and half. If you use the single loop
version of magic loop, you don't divide them. Spread the sts out from the L needle as far around as they'll go, then fold up the cord/sts so the end with the yarn is close to the needle tip, loop the R needle and start knitting.