FOI
Sorry, Rush, BMD will have to go through the complete FAA CFI certification process to get his ticket, including taking the FOI written. 14 CFR 61.183(e) sets forth that specific requirement:
(e) Pass a knowledge test on the areas listed in §61.185(a)(1) of this part, unless the applicant:
(1) Holds a flight instructor certificate or ground instructor certificate issued under this part;
(2) Holds a current teacher's certificate issued by a State, county, city, or municipality that authorizes the person to teach at an educational level of the 7th grade or higher; or
(3) Is employed as a teacher at an accredited college or university. (emphasis added)
Thus, unless he/she falls under these exceptions, the FOI written exam is a requirement.
On the bright side, for one thing, I know the Aviation Instructor's Handbook, upon which the FOI written is based, is derived from the AF text used for the same purpose. So, he probably won't have to study much for the exam and won't need as much prep for the CFI oral as we civilian dudes.
Good luck with your CFI prep.