I went back through my records, and Shayna, my only BP, averages 4-5 months without eating in the winter, and a little over 5 was her longest fast. She has gone 8 months with only a few meals, not zero meals.
When you say "significant weight loss," what do you mean? Shayna will routinely lose 5-8% of her body weight in a fast and then gain it back again when she starts eating again. I set my worry meter at about 10% weight loss.
Having said that, even then, I don't freak out and look at other cues.
Shayna is very inactive in fast and stays mostly on the cool side of the tank. She does not (generally) cruise and certainly doesn't seem like she's looking for food if she does. Occasionally she will urinate (I make sure all my snakes have fresh water always) and towards the beginning of the fast I might get a poop or two.
I take the last known dry weight to measure the weight loss.
I wouldn't try live, yet.
So, in summary, question wise:
1. How much weight has he lost (total and from what weight did he start at)?
2. How's his activity?
3. Is there at least urine and urates occasionally?
As stated before, I trust you on temps, but one thought, aside from a car ride, is to adjust temps a tiny bit or humidity the same. Make him think like things are changing.
Of course, only if your temps aren't near the top of safe range on the hot side (for everyone else's benefit as well).