I've tried a few possible solutions and they don't seem possible. The health regen options seem to be broken when given as a player trait through scripting.
as Sitri has indicated, there should be a way to do this using mimi-game player traits, but if that doesn't work (I personally have not tried) However, outside of this option, it does not appear to be possible to give players health. However, I am experimenting with a way to protect players for a moment after picking up a custom power-up, allowing them time to heal, which effectively is very close to what health is in this game... You might see a post about that soon (if it works)