Yes, it is technically possible, but it is occult knowledge. I don't know how. I know the one Kindle with ads I had, they somehow disappeared and never returned after I reset it, possibly because I did not connect it to any Amazon account or Wifi. You won't get any help with that aspect from any mainstream Kindle jailbreak devs or on MobileRead, as they follow a general policy of live and let live with Amazon. They don't get DMCAs on jailbreaks, they don't help people "pirate".
They don't do that anymore, at least not for me. I tried contacting two different support agents and both mentioned that the functionality has been removed for them by the higher-ups.