don't split the ball joint; it never goes well unless you have the nice handy porsche tool. remove the bolt that holds the control arm to the subframe (you loosened this earlier). that should give you enough play. i don't think you'll need to remove the diagonal link, but i've been wrong before....
you have a better view there; if you think the diagonal link is a problem, remove the bolt in the center of the control arm BEFORE you separate the control arm from the subframe. once you have enough room, use a c-clamp to pinch the upright to the strut (put the c-clamp where the drop link goes). i think you'll get better leverage w/ the SIR tool if the wheel carrier is still attached to the strut.