No-slip on interior boundary

I like to solve (Comsol 4.1) Navier-Stokes (incompressible) in a 2D-domain that has an interior boundary (typically a line starting at some point on the exterior boundary and ending at some point inside the domain). On this interior boundary I like to impose a no-slip condition. However, Comsol does not allow me to do so. It says that this interior boundary is "not applicable". Does anybody know how to enable interior boundaries in order to impose boundary conditions there (I know that this was possible in 3.5)?

Leon