Hey, you can use this idea. I posted a question on Yahoo Answers about the same thing, and someone replied with this:
What you need is some clear vinyl. It's have plastic garment bags and window sticker decals are made of (found at automotive stores). Find the size you want of the circle by making demos with paper. Color in the vinyl of a square shape with some nice markers like Copics or Sharpies in the multi colors rather and the basic ones since Alois' tattoo is kinda pastel ONTO the vinyl.
Spray some "spray adhesive" on top the design. Add another piece of square vinyl on top. This will secure the design from being affected by your saliva. Cut out the circle. Starting with circles to being with makes it harder for you to stick the 2 pieces together, perfectly. You can also cut the inside out but that gives the potential of the vinyl ripping since the design is so close to the edge and thin.
Stick onto your tongue for photos. I wouldn't recommend keeping it in your mouth all the time because your mouth will make crazy tons of spit.
(She's saying that to get clear vinyl, then you find your size you want on the tattoo. Color in the vinyl, not your mouth, the vinyl with good markers in a square shape. Then, use spray adhesive to make the vinyl sticky, then, design it. Then stick another piece of vinyl over the sticky part to hold it, then there you go. It was kind of confusing at first. But, I re-read it again and again. Then I found out.)