How do you make fake tongue rings?

Pretty much impossible. You can fake other piercings with a ring on say the lip, ears, nostril, septum, etc. But with the tongue, you can't really fake a barbell. If you are really into having a piercing without having the piercing, and want a barbell appearance, you can apply silver beads to the skin with a movie grade skin glue called Spirit Gum.

You can purchase magnetic tongue rings online but they can be swallowed easily. So you couldn't eat with them and they might move around.