Adding a Faxen Force on Stokes drag force in Particle Tracing Module

Hi everyone,

I am trying to use the particle tracing module with a non-uniform laminar flow in a channel. I am using "Drag Force" to trace the particles' motion. However, the Stokes force is defined without the Faxen Force in Comsol.
(oi46.tinypic.com/28c33nl.jpg)

I am wondering how I can add the Faxen Force on the equation. Is there already built-in physics module for Faxen Force?

Thanks a lot,
Damla