High levels of some Growth Hormones (such as IGF-1) can also induce double ovulation, so cow's milk from a processed place (such as American milk) can contain high levels of GHs, but the organic stuff won't have that in. Don't think we pump our cattle full of growth hormones, nor does Australia, so that may not help.

Apparently sneezing can trigger a double ovulation, so maybe getting hay fever would be another plan?