I also used royal icing to attach the ribbon and it worked great. It's just like glue. The ribbon was a wired ribbon on a fondant cake. I piped icing around the cake at the bottom of the cake and at the top edge of where the ribbon would go...attached the ribbon, smoothing as I went and piped at the end vertically where the two ends meet. Hope that makes sense!!! Best of Luck.
When you put ribbon on buttercream, does the grease soak through onto the ribbon?
Yes the grease does soak through, depending on the type of ribbon you use. I know that some people have used a coated ribbon, but I can't find it. So, I use wax paper: I cut the wax paper to fit the ribbon and use it as a backing. I attach the ribbon and wax paper to the cake with corsage pins. Hope this helps!! 
I use a non-toxic glue stick, like the ones sold for kids - especially with the latest craze for 'SHEER' ribbons - I just run the stick along the back of the ribbon and 'voila!' it sticks well enough. Helpful hint - seems impossible these days to find NON-WIRED sheer ribbon, so I simply cut the length needed, and pull out the fine wire with a needle-nose plier. Ribbon goes on much easier to cake sides - leaves no 'ripples' - hope this helps
Quote by @%username% on %date%
%body%