Wall slip velocity function possible?

Hello,

I will soon study the behaviour of HDPE melt which exhibits slip at walls. A few questions arise regarding this, mainly and most importantly how to implement a wall function allowing slip following a certain law. I could not find an option to use a UDF for walls. Is this at all possible in Acusolve 2017.1? Modelling another property of HDPE (viscosity model dependent on pressure and temperature) seems to be possible without a problem using UDFs.