A "fresh" leaf will be elastic enough to lay any way you want, collect them and put them in a book in between two saran wrap, or plastic, sheets until you are ready to use them, if you need the leaf to follow a curve then put them in a paperback book that youll curve to the desired shape. You can even coat the top part with epoxy and lay it on the plastic sheet, it will sort of stick to it but not permanently, that way can stay there until youll use them, it will be like a decal: glue to the hull once set peel the plastic from the top.
If you need to flatten, or curve, an older leaf, thats too rigid for the book system, do it on the spot cover it with a moist cloth and iron it, leave the cloth on and maybe a weight (book) or tape it if its on a curve otherwise if you take the cloth off right away it will curl at the edges.
Look into the color change overtime.
(things you learn babysitting two nieces..... although its a good way to turn a cheap 50cents scrapbook into a 15$ one, if you even need to make a gift... or start one of those apparently profitable scrapbooking businesses...)