In my experience natural cues (especially warmer temps) seem to trigger a feeding response/end of brumation. I don't like my snakes to get in the habit of refusing meals, so when they seem to go off feeding, and I'm not intentionally brumating them, I offer food less often. For instance, if they are used to eating weekly, then don't eat, then I'll offer again in a week, if they refuse, then I won't offer again for 2 weeks, then 2 wks after that. If they're at a healthy weight and temps aren't high, then they will start eating when they're ready, and if they're ready 2 weeks before they are offered a meal, they'll catch up over the summer.

Also, I usually get a sense when a snake is hungry, but that's kind of hard to explain or advise and seems to require that I'm pretty relaxed about it.

Best of luck!
Adam