So there will be an external device powering it? Wow, 
I never had a leg implant, but I would consider a larger object to be placed in my forearm.
My skin is paper thin there and I don’t have fat under my skin.
Epidural, laughing gas, morphine… they knock you out, but the side effects are 
The most lido I got injected was about 3ml 1%. That could numb down a rather large area. Plus you could keep aware of the procedure by using lido, unlike with N2O.
I’m almost sure you’ll not get morphine injected. I only got that only a few times (that drifts you to a happy place and puts you to a mild sleep), but the aftermath is rather depressive, so I’d not recommend… 
actually… no.
You’ll do more research anyways and will discuss every step with a medical doctor. The installation of a match box size device is no joke. (maybe bigger?)
But interesting for sure.
Please update me-us about your project!
Note: I have no personal experience with epidural.