I finally did it, reamed out my bottom. I found the right size drill and carefully aligned it with the bottom orifice. I used the original hole as a pilot and drilled very slowly and carefully. The material was some sort of alloy and I plodded on with it, carefully. I kept checking the drill's penetration against the shaft. The little filleted insert went right the way up to the interior of the atomizer. I didn't drill fully through to the bottom of the chamber.
I carefully blew out all and any debris - though most of this had fallen out in the drilling. I checked the sealing ring between + and - to ensure there was no metal lodged in it which would bridge the connections. I put a tiny bit of juice in the atty and... I have a 650 mah Ego battery which is my least used and cherished vaping power source. I used this that on the basis of there being a bang when I tried my reamed out atomizer, this I would shed few tears over.
I fired up. Nothing. Somewhere in the process I suspect one of the tiny heating wire connections either broke or came adrift. The atomizer is now in the bin.