Security :: Single Purpose Ssh Key For Sshfs?

I'm wondering if anyone can give me some guidance, or point me to a relevant reference for setting up a single purpose ssh key.I have setup a single purpose key for rsync, where I have command="/path/to/rsync-secure" associated with the public key in .ssh/authorized_keys, and the rsync-script checks to make sure incoming commands begin with 'rsync --secure', What I would like to do is do something similar to allow sshfs access, and have the server path that can be mounted locked down to a particular location. Does anyone have any suggestions as to how this could be done?As an aside, I might also want to restrict the above rsync script to only allow synchronization to a particular path.