Probit model with specification for the conditional variance

Guys,
 
Is 
there a ready made package/function to estimate a probit model where I can also 
specify a functional form for the conditional variance (something like 
Var(epsilon_i | x_i) = bZ)
 
I can?t 
see how you would do that wil polr (from MASS) or even 
MCMCoprobit.
 
Thanks!
 
//Giuseppe