[Freesurfer] GLM: Define the design matrix by myself

Hello, Freesurfer experts: I want to define the design matrix by myself in GLM, I know that in FS, when we deal with the categorized factors, we treat them as classes, So basically, I want to make a design matrix like this:

1) formula_EffectOnGroupWithAgeGenderCovariates = 1 + TermGroup + TermAge + TermGender and 2) formula_EffectOnGroupWithAgeGenderInterectionCovariates = 1 + TermAge + TermGender * TermGroup

Here, TermGroup and TermGender are categorized factors, so I know that we can make the design matrix like 2) in FS, cuz here we define it as intersection, but my question is that if wen can define a matrix like the first one? I know in SurfStat, we can define it like 1)

Hope to hear from you soon:)

thank you in advance!