Do the mathematics yourself. Or if you can't handle the mathematics, then figure it out logically.
If Kim has to jump from No. 8 to No. 4, then she has to overtake No. 4 Kuznetsova, No. 5 Justine, No. 6 Dementieva, No. 7 Serena.
All except Justine are left in the Toronto tournament. So logically, Kim has to gain as many points as possible, so probably make the finals or win the title to get to No. 4.
Justine is defending points from the Olympics. However, she may gain some points by winning the title beating Mauresmo and Kim on the way, so she will probably need to lose a bit earlier for Kim to have a chance for No. 4.