Tom, it was indeed DisplayConduit that I needed. Specifically, I needed to override the DrawOverlay and CalculateBoundingBox functions. And it looks like it’s necessary to make objects with Rhino.Geometry instead of rhinoscriptsyntax (since rhinoscriptsyntax immediately adds objects to the document).
I’m so glad you saw my thread. I’ve been trying to figure this out for days…maybe weeks. But I didn’t know what to search for or even how to ask about it.
Here’s my sample script to test some sliders.
slider test with solver4.py (5.6 KB)
And here it is in action.