Egg whites will work, but so will water. The water melts the sugars just enough to cause both surfaces to stick to one another... you might need to hold it into place for 10-20 seconds depending on how big or heavy the piece is.

also if you can find it at a local cake supply store look for: gum tragacath, also known as CMC and or/Tylose (approx $7.00) ... you take 1/4 teaspoon and mix this with 3 tablespoons of water, it will be cloudy at first but once its refrigerated for 1 hour it will be at full strength and ready to use (i make mine the night before and refrigerate over night, I find it works best for the heavier items, but thats me... ) if you need it right away, you may put it in the freezer for 10 to 15 minutes to get it cool faster and you can use it but its not at full strength... it'll get stickier as the time goes by... when its at full strength it'll be like a clear glob and while you use it and its out of the frige and the temperature start to get warmer it gets a lil'cloudy, but it goes back to being clear once it cools up again. Store in a container ( i prefer a glass one, but its not what you need to use) and put it in the refrigerator when not using; if you dont run out of it, it's good for 2 weeks.

I used water cause its cheapier But when I started to make flowers and fondant things that are heavier this GLUE is much easier and dries almost immediately.... I LOVE using melted chocolate for my 3D monograms, numbers and much much heaiver fondant or gumpaste characters that need to be upright position... Hope This Helps!