If you get your flowers ahead of time, try different ways to situate them and see how you like them best. Then you can wrap a wire or tape around them to secure the bundles the way you want them. That way there is no fuss later on.
As soon as I got the little vases in the mail, I had to try them out and I just picked some flowers from the back yard to see how they looked. I was really excited about these!
Once you know how you want them, just put some hot glue in the bottom of the boutonniere and shove your flower bunch in there (if they are fake), and hold for a couple seconds until they have set. Easy!