Okay, I dunno if this is gonna make it more confusing, but here it goes. If I come across doing another grille, I'll take some pictures and do a DIY.
(remove the grille from the car and work on a table)
In order to wrap the "humps/bumps" on the inner side of the grill, what you do is first cut out one piece that covers about 1/2 of the grill (to the bottom of the emblem), like in the picture below. Once you peel the backing paper off, lay it on top of the grill and trim out the emblem (or you can remove the emblem first, which will be easier). Then, you squeegee the vinyl to all the "face" of the grill and stretch a bit if necessary so that there aren't any wrinkles. No heat gun needed up to this point.
Then, you make a cut on the bottom of the top horizontal bar (dotted lines). This will give you piece "1" below. Now you apply light heat to piece 1 (start from center) and fold it down (to the top of the next bar) so that the inner side of the grill (i.e. humps) get covered. When heat is applied, the vinyl is very flexible which allows you to shape it around the humps. You don't even need a squeegee, I just wore a cotton glove to press the vinyl to the plastic. The most difficult parts are the inside corners of each horizontal bar. You just need to apply a little more heat than usual and press it down. The corners aren't going to come out perfect, but it's hardly visible unless you really look for them.
Then you do the bottom half. You can probably use 1 large to piece to do this, but it's very difficult with the emblem on and you will need someone to help you stretch the vinyl on all four corners so the face of the grill gets covered with no wrinkles.
