Well I had a little setup home that worked well, not sure if it would help but it was way more simple than machining a 12 tube setup.
I just installed a removable collar made with thing plastic held with an elastic that extended a couple of inches above the nade, filled the top with BBs (I had 204s, so I used a pill bottle as a quick reference for the 200 BBs) and just started jabbing like mad with whatever was handy.
I also toyed with removing the o-ring before filling, it went well with an epoxy sculpting tool not unlike a dental tool. I did scrap a few orings, but they often failed anyway so I had an absurd amount of spares. Besides they are quite cheap and I got to inspect them before use so no more mess in the pouches or dud nades.
Very low tech solutions but it sped up loading a lot.