How can I expose a host directory to a sandboxed bottle?

[waechtjn]

I am running Bottles as a flatpak.

I have a bottle which I want to expose a host directory to (in read/write mode). If I expose the directory via Settings/Manage Drives, I can see it from explorer.exe running inside the bottle as long as I keep the "Dedicated Sandbox" option off. This works with exposing the directory to the Bottles (main) flatpak sandbox using Flatseal as well as with using Portals.

However, in either case, the path is simply empty if I turn the dedicated sandbox on. From what I understand, flatpak-spawn only supports exposing subdirectories of ~/.var/app/$APP_ID/sandbox. So is exposing an arbitrary host directory even supported with sandboxed bottles? How can I do this?