Channelflow Pressure Boundary Conditions

Can Channelflow easily switch to a Neumann boundary condition for wall pressure?
The Dirichlet boundary condition currently imposed keeps the pressure during a Couette flow at zero on the wall and causes the pressure to dip below zero (to -0.5 Pa) in the center. You can easily veritfy this by running:

randomfield -Nx  65 -Ny  33 -Nz  65  -Lx 10 -Lz 10 -m 0.001
simulateflow -nu 0.000016 -T 100 -dt 0.004 -vdt false -dT 1

I was hoping to study the stability of Couette laminar flow and turbulent flow for which the normal dP/dy=0 (Neumann boundary condition). Wouldn’t dP/dy=0 at the wall be more physical?