www.webexams.com
Didn't take it with the FSDO, but did mine down in the Vegas area. There are a few DEs I saw do rides while I was down there for CFI ratings, and they all seemed very fair.
Remember, you aren't just answering questions, you are teaching the subject. So show you can teach. The examiner should be clear as to when they are a 'student' you are teaching, and when they are looking for a simple answer from you as a CFI applicant.