Ah, the string descriptor stuff might not be public, now that I'm looking at it.

If you give it a try and run into any problems, just open an issue and I'll get it sorted.

https://github.com/jamesmunns/postcard-rpc/blob/main/source/postcard-rpc/src/server/impls/embassy_usb_v0_3.rs#L100-L156
is what you need to copy + customize