If you intnd to train in a fasted state its almost imperativeyou take in, as per LeanGains, 10g BCAA's prior to a workout. Other than that this is where Im gonna say its trial and error. I highly doubt a dose of aminos is gonna affect insulin sensitivity later when breaking fast. A lot of this is hormonal inductions for catacholamines, IGF, and insulin.
Theres a really good article somewhere around here on the cortisol/insulin fiasco that happens via breakfast. I start work at 6AM and wont break fast until 4PM when I get home. Made life a lot easier. I do take in about 6g beef aminos around 12 though.