Boortz and Linder didnt design the fair tax they are simply the supporters of it that have a national voice.

From Boortz's book: the fairtax was designed by a Houston businessman that was pissed about business decisions made based on tax considerations more than profit considerations. He started fairtax.org(not the name at the time) and after a few million in donations was made he asked several major universities for their proposals. After they had their proposals economists went over the proposals and with the aid of focus groups and polls worked out the basics of the fair tax.

Thats not a quote of the book as that was about a page and a worth, but its basicly how it happened.