Pre-soak the foam in your elegant bridal bouquet holder using warm water mixed with floral preservative.  Be sure to fully saturate the foam so that there are no hidden air pockets.  Using the plumosa partially cover the foam cage and conceal your basic mechanics.  Easiest is to use one long stem, insert it into the foam and then just wrap the frond around the holder tucking it into itself to secure.  If you need to, you can anchor it in place with a wire hairpin.