Combine mkfifo and cp --reflink to append files without copying data

I have huge files {0..9}.bin which I want concatenate into out.bin. I don't need the original files afterwards. So I was wondering, if this is possible by only modifying the filesystem index without copying the file contents (see https://unix.stackexchange.com/q/80429/234981 for efficient copy solutions). On modern file systems (e.g. btrfs) cp --reflink=always exists. Fifos are on the file system level (at least btrfs send also tracks fifos), so they should have information about the actual data blocks used. Therefore, cp --reflink=always should be able to determine the extend numbers on disk and re-use them. So I was wondering, if it is possible to use mkfifo in combination with cp --reflink=always? **Update** Currently, it is not working:

for i in {1..9}; do dd if=/dev/urandom of="in$i.bin" bs=5M count=200; done;
mkfifo fifo
cat in* >fifo &
cp --reflink=always fifo out.bin

results in cp: failed to clone 'out.bin' from 'fifo': Invalid argument Probably, it never will, since FIFOs have no information about the storage origin bug instead are just dumb pipes.