[kken]

This is a nice hack.

BUT: This has been done years ago for under $1 (the price of a nRF24L01 board) by using a nRF24L01 itself.

http://travisgoodspeed.blogspot.de/2011/02/promiscuity-is-nr...

[timthorn]

But not for Bluetooth LE, I think?

[kken]

I am not sure, that is a good question. People have shown that it is possible to hack a nRF24L01 into sending BLE transmissions. But there are limits. It could be possible to sniff parts of BLE traffic.