In case anyone, like me, stumbles upon this because they have the same question. I just found the answer:
Place text above rectangle
Open Blending Options of text (by double clicking the layer or right click->blending options)
Under Advanced Blending you’ll find the “Knockout” option:
Set that to shallow (to knockout just the layer below)
or deep (to knockout everything until it reveals the background layer)
Reduce the fill opacity to 0%
done! Hope that can help someone 🙂