The aerosols affect drop number in clouds, which (A) affects the radiation with different numbers and (B) results in different cloud microphysics evolution and cloud lifetime. It is hard to remove these.
You could fix the drop number in the radiation code (we don't support this, but it could be done), but that doesn't change (B).
Alternatively you can fix drop numbers in the microphysics with namelist variables (search on nccons) to remove all indirect effects (which may be what you want), but this is a slightly different model, with potential impacts on anything related to cloud microphysics (Cloud radiative effects, precipitation, cloud feedbacks).
Hope that helps.
Regards,
Andrew