I really love the idea of creating a fun, interactive mailshot- to give a promotional preview into my product and all the quirky wonderment I aspire it to offer.
Although not necessarily original, I like the idea of the "cut out and keep moustache"- almost a free gift and an instant smile inducer, thus creating a positive connection to the idea of moustaches from the start.
I quite like the idea of designing the moustache around a postcard- contained within, looking quite ordinary to begin with, but charming and fun when you discover the "cut out and keep" element.
Perhaps with a tag line such as "reason #1: Because you've got one too"... leading onto text with directions to find out more... (perhaps a link to a web page, or title of the book?)
Designs coming soon!