Add fixed effect row to tab_model from sjPlot (r)

Question

I am trying to add rows to a regression plotted in sjPlot using the tab_model function. I would like to add rows beneath the predictors, which I fill with an "x" if the fixed effect is present, and leave blank if not. These would be for year and country fixed effects. I am using a fixest regresion.

If my regression is the following:

library(fixest)
reg2 <- feols(data = mtcars, mpg ~ vs * (am + hp + carb) + vs * (disp + hp + carb) | gear + carb)

and I use

library(sjPlot)
tab_model(reg2)

Is there an argument I can add to the resulting table to make these custom rows added? The row names would thus be "gear FE" and "Carb FE". So in different iterations of the original reg2 (with or without "carb" and "gear"), x's would fill in the table row, or not.

EDIT

The desired addition to the table would resemble the circled row within the following table: