I've had luck "forcing" splits when I wanted to by (gently) inducing stress. I've never done it with temperature like you're describing, but I've often noticed they'll split if you change things in their routine - i.e. feed them every day for a week or two, then totally stop the food and they'll split within a few days. Of course you need to keep their health as a priority when doing this...
Then again they've pretty much always split like rabbits for me, I've never really had to try. In fact the constant splitting is why I don't have plans to put one in my big tank, I don't want a million little clones climbing all over the place in a year or two.