So, to extrapolate, ghouls can hop into the NeverNever via mass graves? Butcher shops? Deserts (they do originate in pre-Islamic Arabian mythology)? Maybe the Alphas might learn to do so via "wild places?"
I have no idea what to do with Ghouls. I'm inclined to suggest that a necropolis, graveyard, or a mass grave (as you suggested) would work, but that may be my association of them with ghouls as portrayed in Lovecraft and D&D.
Returning to the idea that this type of passage is made possible by sympathetic associations and spiritual energy, and dissociating Dresdenverse ghouls from the strictly undead variety in other fictions, I come back to thinking that places of large-scale murder or death would make sense. So, yeah: mass graves; butcheries; places where a plagued caused a quick, painful death for many people; execution rooms that get a LOT of innocent clientele (presumably in third-world dictatorships).
If we went for things which literally resonated with the unending ghoul hunger, then butcheries would make sense, but we would also have them appearing in places of acute gluttony, like all-you-can-eat restaurants, which doesn't seem like it would really fit.