toast useless

create table test(x integer, y integer, w varchar(50), z varchar(80));
When a table has well defined sizes all their data is stored on heap, so
they doesn´t need to be toasted, and no toast table is created. Fine.

But then I want to store last modification of that record, so I do ...
alter table test add audit_last_record jsonb;
And a trigger to store old.* on that field.

So I'm sure that jsonb will fit on heap too because their size is all other
fields converted to jsonb, never bigger than that.

But as soon as I´ve created that field, a toast table is created too. Even
if I set storage MAIN to that field, reltoastrelid on pg_class still exists.

alter table test alter audit_last_record SET STORAGE MAIN

So, there is a way to eliminate these useless toast tables ?

thanks
Marcos