Another option is to go the recertification route - you're allowed to recertify with the MD every 30 days for intermittent. What I do is attach a copy of the employee's attendance record and ask for the doctor to verify that (1) those dates/times were for FMLA, and that (2) the pattern of FMLA use is consistent with the diagnosis.
"You are you. Now isn't that pleasant?" -Dr. Seuss