in the end pin0 - pin4 are simply Micropython variables, so either switch to the Micropython tab or use Execute code blocks to add more pinX variables.
Well that's really unsatisfying, and an M5Stack failing - they appear for older devices but not the new ones.
Now I've got some super disappointed kids, programming in code still a little beyond them. They were excited about the DIY camera. M5Stack, you listening? :)
@felmue thank you very much. I go to try that. In the mean time I discovered that the function cardkb_getstring covers more or less what I wanted to achieve.