There are many ways to do this.A way to drop a fake rune is to cast Astral Imprisonment on a unit with Linkens Sphere's buff and a fake rune will drop.It will have the effect of a Double Damage rune and will look like a Double Damage Rune, but you can not take it.
i don`t know if it is possible now in the newer versions.
If you are SK with bottle, you pick a rune in your bottle, you wait 1min59, and you impale exactly at the 2'00 mark, you'll drop the rune. If you are any hero with a rune in your bottle, you don't use the rune, and you get impaled by NA exactly 2'00 after you picked that rune, you'll drop it. nab topic, close it!