I'm so sorry to hear of Charlie's horrible accident.
The fact Charlie is paying attention to his paw is a good thing, even though he's causing himself damage. The way I see it, and I'm not a vet, is the paw is starting to tingle, making him try to stop the "itch". Of course he can't, so he continues to chew it in futile hopes it'll stop.
I would think that acupuncture would be a viable alternative to help with the tingling. I think amputation is a bit premature at this stage. After all, it's only been 5 weeks. I think he's made remarkable progress and deserves to see if the feeling comes back. Please think of acupuncture before you opt for amputation! There are many people who swear by it! I'm sure your vet could direct you to someone in a place of authority who could provide information about it, since your vet can't. Good luck and please keep us posted on his recovery!