I am doing my first wedding cake. The bride showed me a few pictures of ideas. One was a cake that had real navy blue lace ribbon attached. I quickly saw that it's a fondant cake. She wants a buttercream cake. My question... Is it possible to put a real lace ribbon on a buttercream cake? If so, how do you accomplish this without the buttercream seeping through the wholes in the lace of the ribbon? Thanks for any help!

It will work if you place a strip of wax paper under the ribbon.  I did this when I was using burlap as the trim.  Wax paper will block the grease from seeping into the ribbon.