Buy 3 different sized clear cylinder vases, a bag of white/tan rocks (or just pick some up outside), 3 fern leaves, 3 flat round candles in either a light green or tan color, lastly fill with water! All these items can either be bought at Michaels
Love the idea of bending the lillies down and attaching the brooch. Could also wrap lace around the glass vase to get a more vintage look and cover up some of the green stems - I'd add large, black ostrich feathers.
Beautiful center pieces or just around the house- rocks, flower of your choice (maybe string it to a rock by the stem so it doesn't float) in a vase, fill with water, add small candle and voila-on the mantle?