Somewhere I have an old rip guide setup doc that shows how to create a spacer of the same thickness material as what's being cut to let you cut stock narrower than the guide rail.
All you do is set the stops tight against the guide rail bracket & then cut your spacer material. Next move the stops left to the width of the part you want to cut and using the spacer cut your stock. Presto, narrow stock guide, save the spacer for later use.
Will try to find the setup guide and post it. (EDIT: Posted below)
RMW
PS - nice job on the guides, I like that they are totally DIY and don't require any machining.