Harman Reflashing Cortana Image
Pre-release
Do not attempt to flash any other image than the one mentioned in the instructions, they will brick the Invoke even worse, as they are not for the Invoke, and will make it currently unrecoverable, possibly needing hardware mods to recover from this type of brick. I have already bricked a spare Invoke from experimenting.
Initially provided by Reddit user theace69 and later officially posted to Harman's support website, this archive contains the tools and instructions to reflash your Invoke back to a firmware that includes Cortana. I would recommend using Linux if possible to perform the flash, you will need to run the run.sh file as root, as I had issues with Windows detecting the device properly, probably due to the rapid disconnects/reconnects the Invoke does while booting into flashing mode.