A client needs to completely disable bluetooth. The most basic level (aside from physically disconnecting the antennas or removing the airport card) seems to be disabling the kernel extensions.
I looked in
/Volumes/<your system's drive name>/Library/Extensions/ while in recover mode, courtesy of this question, but there were no bluetooth extensions there.
/System/Library/Extensions/IO80211family.kext will disable wifi, but I also ran into issues trying to delete this without being in recovery mode. (Recovery mode shows this file in
/Volumes/<your system's drive name>/System/Library/Extension, and wifi was successfully disabled after deleting that file from within recover mode, showing
No Hardware Installed after rebooting.)
What file should I delete to achieve the same result for bluetooth?