I couldn't find a way to use some key sequence to make 789/uio/jkl/, keys work as numeric keyboard equivalent, so I created them in BTT.
Holding fn + ctrl
will map 789/uio/jkl/, keys into number equivalents, while additionaly holding shift
(fn + ctrl + shift
) will read the number out loud + show the BTT hud with typed number.
You can get the JSONs for the actions here: https://github.com/Worie/btt-presets/tree/master/numeric-keyboard