Hi @davidbozo,
Welcome to the Auth0 Community!
You should be on the right track with a Post-Login Action, as there is the option to use Event Object to get the Device Code parameters.
This being said, while searching a bit on this matter, I believe that currently it’s not possible to pass custom parameters to /oauth/device/code like you can on /authorize ( limitation has been mentioned on this page ) and you need to use a custom scope value instead. Please find this Knowledge Article which explains in more detail.
If you would like to, you can leave your feedback to bring this to the attention of other users who might be looking for this feature. If there is a wider interest, development on the matter can be made in order to implement this functionality.
Hope this helped!
Gerald