@akadaedalus: That unfortunately depends on the device, and this only affects powering up/down the chip, which is only less than half the battle (and apparently, doing it wrong breaks Nickel's own handling of it, c.f.,
https://github.com/koreader/koreader...r.sh#L192-L206 which successfully kills it, but apparently kills it for good

).
c.f., arch/arm/mach-imx/imx_ntx_io.c (or similar, moves around depending on the kernel).
Code:
#define CM_BLUETOOTH_PWR 126
(I haven't looked into this any further)
EDIT: There's a /bin/ioctl binary on Kobo FW, but I have no idea of its provenance and whether it deals sanely w/ by-reference vs. by-value ioctl shenanigans...