How long with no food?

[Bogertophis]

Also I do frozen thawed, so im not sure the shavings trick would do much

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Helps more than you might think. Thaw the rat in cool water...it washes off more of the rat scent. Then add scent of mice & warm to "lifelike" warmth* (which I assume you've been doing?) & use tongs to slightly
wiggle rodent AWAY from the snake, never towards the snake. (rodent in the real world don't volunteer to get eaten, & if they appear to do that it may scare your snake into not eating)

Timing & "atmosphere" can also help get a snake to eat: BPs are ambush predators, & usually like to strike from their hiding place at rodents that appear to be cluelessly passing by, in the evening, dim lighting.
You don't want to offer food to a BP that is out cruising his cage...they're too cautious to eat in the open like that, usually.

All of these seemingly tiny details can seriously make a difference...especially offering the prey WARM -about 100*- just not cooked though. And I agree w/ Craig...keep a young snake eating, work out the details
when they're older & have more body size. Don't go too long before you just offer what HE wants.