Coupled displacement boundary condition PDE Toolbox

Hi, I am making a simple structural analysis of a coated airfoil piece with PDE Toolbox.

I use 3D since plane strain/stress assumptions don't suit my problem. So I have a sector of multilayered cylinder (in XY plane). I set roller boundary conditions on the angled sliced sides (radial faces, perpendicular to the XY plane) and one set of faces on the axial plane parallel to XY plane.

Since I want to represent a periodic structure I need to constrain the other part of the geometry - set of faces paraller to XY plane, which was left. I need to set their Z displacement to be equal for all the faces on that side. I want to allow these layers of material to move in the Z direction but only all together, so this side remains flat. In ANSYS this works if you create a rigid plane, which can move only in normal direction, and tie all the faces wanted to this plane.

I have searched through all the available boundary conditions but didn't find any suitable. Maybe to write my own, but I am not that advanced in it yet.

I will kindly appreciate if you can help me out on that.