Lapageria, a forest native of southern Chile, prefers acidic, organic, damp, shaded, cool, well-drained soil.
I wonder if there's a suitable native groundcover to match. What smaller plants grow around Lapageria in the wild?
Probably nothing much grew beneath it in its native habitat - it grows in forests and is a twining climber, so it will likely scramble up trees and head for the light. It prefers partial to full shade anyway, so best planted where that can be provided.
If you want to know what to plant in front of it, azaleas spring to mind, provided you're not in USDA zone 10 or above.