Plotting conditional effects for sub-models in a non-linear model

Is there a way to use the conditional_effects() function to plot the effects of factors at all levels of a non-linear model? For example, in the following model

y ~ var_a + var_b + var_a:var_b
var_a ~ var_c + var_d
var_b ~ 1

I’d like to be able to plot the effect of var_c on var_a using the conditional_effects function in brms. While I can plot the effect of any factor (var_a, var_b, var_c or var_d) on y, I haven’t found a way to plot factor effects for any of the “sub” responses. Is there a way to do this using the conditional_effects() function? If not, is there another function that makes this possible, or does this require a more manual approach?