I hope you have some old bottles, caps, and a recapper. I have a collection of original coke bottles in storage (bad by now to drink) in various sizes.
The bottle machines are quite cheap now as it's almost impossible to get them unless you have a specialty store nearby. You might try filling it with something like Jones Soda with the twist caps. I've been told those fit and they have a ton of "interesting" flavors. They sell them at our local grocery. (Yes I know most here would just fill it with beer etc)
Seems like NoVArcade has your schematic mod covered so I won't add to that.