Dear Miss S:
Most of us think of a book as a front and back cover with pages in the middle. I am readying a proposal for a non-fiction book, but its production must be -- by necessity -- a little off the wall in something of a medium-is-the-message statement. I envision the book as loose-leaf 3 X 5 index cards nestled in a file box. (OK, it's a diet book.)
My question: Should I go to the trouble of doing a mockup? I would offer in the proposal to send the mockup upon request. The mockup would essentially be the finished product without the slick printing and packaging. My first thought is that this sounds amateurish, but it certainly does get the concept across quickly.
(I searched for your balloon in the Thanksgiving parade to no avail, but I thought at one point I did see a giant Killer Yapp!)
All sorts of things are masquerading as books these days. Those elves in the production department are really Bright Young Things and full of great ideas.
That said, you don't want editors to reject your work cause they don't think they can sell the packaging. You're offering content, not package. If Production wants to make the book into a scale model of the Eiffel tower with receipes hanging off the side like wings, your only response, is thank you where's my advance money.
I have people send me queries with production specs more often than you think. I almost routinely say no because I don't want to fight with them about why the editor will buy content but not production.
If you really really really insist on your own version, you're going to be happier doing it yourself. On the other hand, diet books are a huge category, and after Thanksgiving Miss Snark herself is rolling through the aisle of the local feed and seed looking for "Dieting for Dirigibles".