I think piping gel would be strong enough to attach it. I would do that while the fondant/gumpaste was still soft. You could also put in a toothpick to the one and let it dry and then put on the cake.
Should just stick onto a fondant covered cake with a bit of water on the back or you could use a glue mix made by letting a bit of fondant sit in a small amount of water till it desolves into a thick paste.
I always use royal icing to attach heavier decorations to fondant cakes and it works great!
Perfect, thanks again!
Melted chocolate works very well on heavier pieces as well.