Starfox
Hero
I believe whenever you force movement, it can only be through an unoccupied square. Otherwise, Rogues would be sliding their foes inbetween their allies and constantly getting combat advantage with every attack.
Emphasis mine.
Correct me if I'm wrong, but nothing in the current rules prevents sliding, pushing, or pulled through an enemy through an enemy-occupied square, as long as he doesn't end up in that square?