Random parameters in bayesmh

Hello,

Could you please advise how to specify the independent variable "x2" from below as a random parameter?

bayesmh z x1 x2 x3 i.id, likelihood(normal({Sigma1})) ///
prior({z:_cons} {z: x1} {z: x2} {z: x5}, normal (0,1000)) ///
block({z:_cons} {z: x1} {z: x2} {z: x5}) ///
prior ({Sigma1}, igamma(.001,.001)) ///
block({Sigma1}) ///
prior({z: i.id}, normal(0,{Sigma2})) ///
block({z: i.id}, reffects) ///
prior({Sigma2}, igamma(.001,.001)) ///
block({Sigma2}) ///
exclude({z: i.id})

Thank you,

Justin