The standard 4-speed auto never even came with a manual mode at the shifter, so it's not equipped for any sort of manual shifting in general. They sold the Demio in Japan (not sure if in other markets) with an optional 7-speed 'sport' CVT. Those had paddles, and some seem to have included a manual mode* on the automatic shifter in addition to the steering wheel controls. They're weird paddles, though. There were two on the back of the steering wheel that would shift up and two buttons on the front for shifting down. I guess so you could use either hand you wanted for up and downshifting. They're similar to the paddles/buttons on the automatic NC MX-5 steering wheel.
In short, you'd need a car equipped for it, or ALL of those parts. You'd need the CVT gearbox, the electronics, the shifter/console, steering wheel, etc. It's easier to just have the whole car. Paddles wouldn't really do much for the standard 4-speed auto anyway.
For fun, though, here's a 0-100km+ run in a 7-speed CVT Demio.
*edit*
Here's an example of the automatic shifter with manual mode.
*edit edit*
Apparently that shifter assembly is from a Mini Cooper and grafted into the Demio console. Not sure if it's functional or not.