Can nipype create an fsf file just for preprocessing?

I am using the FSL interface in Nipype for fMRI analysis and having a hard time creating a feat-specific file for preprocessing. Specifically, what I would like to do is:

  1. Create a fsf_file using custom parameters for each participant
  2. Loop across all participants and run preprocessing for each using fsl.FEAT() and the fsf_file from step 1

In a previous workflow I have created an fsf for a level one analysis using model.SpecifyModel() and fsl.Level1Design(). However, I can’t find any guidance for how to perform the same function as fsl.Level1Design() but running only pre-stats.

Looking closely into the nipype directory, I can see in /nipype/interfaces/fsl/model_templates that there is a model template, feat_header.tcl, which would allow me to change which stages are run by FEAT by accessing $analysis_stages:

# Which stages to run
# 0 : No first-level analysis (registration and/or group stats only)
# 7 : Full first-level analysis
# 1 : Pre-Stats
# 3 : Pre-Stats + Stats
# 2 :             Stats
# 6 :             Stats + Post-stats
# 4 :                     Post-stats
set fmri(analysis) $analysis_stages

However, there is no script in the fsl interface that can be used to access this template. Am I missing something crucial here? How can I create an fsf file for preprocessing and run this in FEAT without running preprocessing node-by-node in a workflow? Thanks, I appreciate any advice.