Multiple Ambitus for Multiple Voices

Hello, I'm trying to replicate part of a published score that has a stave containing two voices, with two ambitus. I was able to configure one ambitus, no problem. Adding another is proving tricky. I added a zero-width frame and imported a PNG image of the second ambitus as a workaround, but the image doesn't import the quality well...any ideas on a trick or suggestion I could try?

Absolutely no urgency, just trying to learn more and thought someone might be more clever than I--thanks!