Electrostatic Boundary Value Problem with 3-D Boundary

Hello,

Does anyone know if it's possible (and how) to solve a boundary value problem in Cartesian coordinates with a 3-D boundary on one face (let's say the z=0 plane). For example, I want to solve Laplace's equation in the domain 0<x<L, 0<y<L, 0<z<L, with Dirichlet BC's on all but the z=0 plane, and have several (let's say two) cylinders of length L_cyl protruding into the domain that also have Dirichlet BC's on their surfaces. Is that possible in the MKL Poisson Library?

Thank you,

Ryan