Note: make sure you have bombs to kill yourself to get back on the map!

On Backlot if you spawn in front of the construction building turn right, go all the way right and you should see a trash can.

Jump on the trash can then over the wall.

From there you will be in a grass area.

Find any dark spot then jump into it, you will not die.

Keep running until you automatically fall off the dark spot.

So you'll then be falling forever.