de embeding S parameters in waveguide

Dose anyone know how to de-embed S parameters of waveguide parts of two side of a sample? (attached figure) I want to de-embed S parameters of the central part from that of the whole structure, but I have no access to inside of the waveguide to set ports in it.
the easiest way is to remove the sample from center and connect to sides of WG the you have T1*T2, and the shorten one side of this new (T1T2) part and have some equations to be solved, (8 eq. 8 Unknown) but it is too time consuming. is there any other way?

Use MatLab..
There is a de-embedding tool for s-parameters...

Yes, there is. but the problem is producing S1 and S3 when we have no access to the internal parts of the waveguide.