I used to be in charge of cleaning these beasts for a very small micro years ago. We would drill a hole in them using a paddle bit and pry them out, another brewer told me he used a slide hammer. Either way, the bungs were trashed when removed.
Where there is a will there is a way. It you want something to reuse the plastic bungs might not cut it but might be able to pull it off with a black rubber stopper.
Drill a hole in the center, thread a stainless eyebolt with a nylon washer and stainless nut on each end, insert and tighten the nut causing the stopper to expand, same logic behind those little sanding manderals on a dremel. To remove, loosen nut and pull out via the eye bolt.