Set it on rollers, when it's fully dry leave it all in. Use ur blow drier on the individual curls, while still hot take the roller out, and use the flat irons to curl it, really over twist the curls so the hair has been wrapped once while you pull it down.
If that's not enough, lightly spray the hair with hairspray section by section as you get to the flat iron part, once curled barrel curl them back up and clip to the head to let them cool, do this all over the head then give a really good spray with hairspray and pop under the hood or use te dryer without a nozzle on a low setting for 5, let cool. Then finish with a fine mist shine spray.
Take it all down and see how long it lasts, on the wedding day, leave it up in the barrel burls until the last minute so it lasts a bit longer.
Hope this helps, it's what I do to my cousins as hers is so heavy and thick it used to fall out in about a hour xoxo