If you do a s-parameter simulation by placing a black-box that will represent your momentum block (or directly itself) you can create touchstone or citifile format s-parameters.In this case, all ports should be 50 Ohm..
1. You can do it either from schematic or data display window. Select "Tools -> Data File Tool" from the menu, a data file window will pop-up; then choose write data file from dataset; specify filename and file format as touchstone; select the dataset you want to export.
2. You may also write an equation in the data display window using the write_snp function. For example,
y=write_snp("spara.s2p", S, "My S-parameter file", "GHz", "MA", 50)