Go to the help room on the right wall - there is a big box, then a gap, then 2 boxes stacked on each other.

Put your back on the far left end of the bookshelf then sprint to the gap, jump into the wall behind it, then kneel while you are in the air.

If this has been done correctly the zombies will not come near you. Also, do not move the left thumbstick or you will get out of the glitch and where you start running does matter.

PS: After a while the zombies that are in the big crowd will start killing each other. The way to tell if it is working before the zombies get to you they will stop periodically and shake their heads.