Interesting.
I see that the Kessy System uses 125kHz ( I am guessing that is the HiTag )
Also 315MHz and 433MHz which I am guessing is the proximity freqs.
So I don’t think you will be able to what you hope to with an implant.
I hope I am wrong, but fear not you still have some options.
If you want to install an aftermarket proximity system, or already have a factory system.
@turbo2ltr made an awesome solution for this
Otherwise, If you keep an eye on @darthdomo CaRFID project, that would also be a great option for you.
Keep us in the loop we love to see people and their projects succeed.