This is a bit late to the party, but I found a 1979 paper on botulinum growth and toxin formation at pH values below 4.6, so somebody found a way to grow it, but the growth conditions in the reference seem irrelevant to the case at hand -
"growth and toxin formation by C. botulinum can take place in homogeneous protein rich substrates (containing 3% or more soya or milk protein) at pH values lower than 4.6"
In this recipe, the vinegar will get the pH rather lower than 4.6, though I would make sure that all of the peppers protrude into the vinegar and have a surface that is conducive to vinegar absorption, remembering that the vinegar will be on the bottom and the oil on the top. I would also prep the peppers by torching them to char and then remove the shiny outer skin (which is pretty impervious to both oil and vinegar). Torching also makes the peppers soft enough to be flexible so that a small spoon will easily fit down into the part where you are trying to remove the seeds. I can also envision a long handled, sharp edged spoon with a rounded end that might be made by grinding down the business end of an ice tea spoon and bending it over just enough to make it into a usable scraper. I have one that is a bit larger that I use to remove seeds from winter squash and melons and papaya. For this use I would suggest a blade radius of no more than ~5mm. A bar spoon might be another good place to start.
For a slightly smaller individual serving size, you might look at using a yellow Fresno chile (mostly because of its size) but they are pretty mild so adding some finely chopped Serrano chile to the filling would be essential.
