This seems like it could work, at least on paper. 98-99% Benzocaine powder is fairly easy to procure in the US, and it is fairly inexpensive. I think I will go ahead and acquire it.
My understanding is that Benzocaine is metabolized in the liver (CP450 metabolism) and the methemoglobinemia is largely caused by several metabolites as opposed to benzocaine itself, so I wonder how much variability there could be between individuals, many things such as diet and any drugs taken concurrently could affect the rate at which it is metabolized.
For reference, this article identifies the main metabolites that cause the production of MetHB: doi: 10.1080/00498254.2016.1196402.
I definitely want to try and document as much as I can of my own attempt as this seems to be a promising method, and it is definitely more accessible than SN or KN, I'll have to think how I can go about that, however