Concept:
nc -lp 1234 -e fusexmp_server
nc 127.0.0.1 1234 -c "fusestream /mnt/tmp"
Advantages:
nc -lp 1234 -e fusexmp_server&
fakefusestream 127.0.0.1 1234
% ls
bin lib usr proc etc
% get /etc/hosts
% exit
Like simple RPC of FUSE methods. The protocol should simple like IRC and should handle all things FUSE can handle.
Is there already such thing or should I implement it?
It seems that ccgfs might help you in that direction. You would run ccgfs-storage on the end where the files are, and ccgfs-mount where the mountpoint is supposed to be, and either of the component is replaceable by a program of yours, presuming it adheres to the stream protocol (doc shipped in tarball). Note that you still need to connect the two components somehow (as in: you decide; it works with stdin/stdout).
socat (preferable to netcat) works with that too.