[Kwant] PBC to OBC conversions on Hamiltonians

[Haxxx Akxxx]

I have k_x k_y k_z dependent PBC hamiltonian(2x2). And I want to go from PBC to 
OBC by limiting size along y such as N_y=5 and have a resultant 
hamiltonian(10x10) PBC-OBC-PBC. In kwant can we do such things?