How to create .fsf design file in Nipype without .nii file

I’d like to create a .fsf design file by loading in my subject information, but without the .nii file. In FEAT I can do this under ‘full model setup’ by manually loading in my files for each regressor and selecting ‘view design’, and then I can save the files. However when I use nipype to automate this for all participants, I can’t create my level 1 design because I’m unable to run modelgen.SpecifyModel() without loading input for ‘functional_runs’. Is there any way to create the .fsf file as I do in FEAT using nipype?