If you absolutely have to, I would suggest establishing the FUSE mount on the Proxmox host and then using a bindmountpoint (e.g. "mp0: /path/on/host,mp=/path/in/container") to make it available in the container. If you establish the FUSE mounts inside the container, you will run into problems (lxc-freeze is not compatible with FUSE which means no snapshots and no suspend backup, you need to change all sorts of containment settings which lessens security, ..).