this is not something ive done / thought of so i may not be fully understanding,
but a couple things that may help
first, i do not think i have a built in mechanism to add a field to a type's
toJson if that field does not exist on the type itself
i expect a custom `toJson` is needed, and currently adding it manually as a
string would work
another possibility is considering either `Table[string, string]` in the toJson
if that fits, or if the object is not super complex, having an internal type
that exists just in `toJson` that copies the values of the outer type and adds
the field before toJson'ing that
if you were willing to take a moment to put together a single file little
example for me i would be up for thinking more about this with more
understanding but npnp if just experimenting for now