yeah, optimization can be a pain :-)
if inlining doesn't cut it for you (depends on theme and plugins used really), you could indeed try deferring, but splitting CSS is to be done by hand. the first part should contain all CSS (or as much of the CSS for) needed to render the page above the fold. There is no easy way to determine what the CSS is, I'm afraid.
That being said, don't focus on "pagespeed score" but rather on real page speed tests using http://www.webpagetest.org/.
frank