How to route a line-in to an output alongside other audio streams?

Since switching to pipewire for lower latency (it really is excellent!) I’ve noticed something which is annoyingly missing. I cannot route line-in ports on the back of my PC directly to an audio output. My main reason for this is to plug in my bass guitar head unit to get audio from my main speakers alongside a backing track. Does anyone know how to loopback an input directly to an output under pipewire (with reasonable latency)?