This app was mentioned in 5 comments, with an average of 2.20 upvotes
There's actually an app that lets you preset combinations of all the sodas and then you just hold it up to the machine to scan a barcode or something and boom, instant custom soda.
It should come with this preinstalled.
Install this app on it
E: ignore the bot, https://play.google.com/store/apps/details?id=com.cocacola.droid.pushplay