Is it possible to write a macro that acts like namespace-set-variable-value! for implicit forms?

[Sage Gerard]

I'd like to use `eval` in terms of a restricted namespace including
`#%datum` and `#%app`. For minimalism and security, I want to build that
namespace starting from an empty one, without using racket/sandbox,
security guards, or attaching racket/base.

Under these restrictions, I would normally attach a custom module
providing only what I care to expose to the code under evaluation.
That's not a problem, but is it possible to avoid creating the extra
module and imperatively attach implicit forms? I'm thinking of a macro
that behaves like `namespace-set-variable-value!`, but allows implicit
forms.

--
~slg