Turn that impossible situation into profit!
Well there's a chance to triple your profit! Tell the bride that the hydrangea bout will last for an hour, but you'll gladly supply someone at her disposal all day that will keep making fresh hydrangea bouts as the previous ones fade!
You could charge her $20 per hour for about 5 hours, pay someone $8.75 to make the bouts throughout the day and you make about $10 per hour for doing nothing.
Now that sounds like a successful hydrangea plan to me.
And I kid you not, I did this last year for a bride who said she wanted only hydrangea. I warned her it doesn't do well in bouquets/bout/corsages, but she insisted on having them. I told her that the only circumstances I would make those bouquets for her would be if she hired me for the day, and paid upfront for 3 bouquets. On her wedding day, I kept making fresh bouquets as her old one would fade and look like an old kleenex...
All the other suggestions are great: hydrate the head under water for a few hours, CG if you have some left (I don't and I'm pretty upset), and do pray to the flower Gods.... Some say it works!