Noise gain to internal vgs using AC analysis

Hi,

I have attached BSIM equivalent model. I want to know the (transresistance) transfer function from drain channel noise source to the internal vgs of the MOSFET (Not between external G and S but internal vgs excluding Rg and Rs drop) in a particular circuit.

I know how to use pss+pnoise+noise separation but I can only choose external nodes. Is there a way to put AC current source between internal drain and source and find gain using AC analysis.