First off, this may only work for Goblins and maybe Gnomes, but if said goblin/gnome has a 2 person mount, you can bring other people through.
Go to this cave in durotar at 53,28:
Get on top of it like this:
Then you should be able to squeeze through if you run around and sidestep a bit where the gap is biggest:
Anyone can click your mount if you stand just on the other side to get through.