How to get automount and sshfs (osxfuse) working with yosemite
FWIW, if anyone else stumbles across this old question, the best guide I have found for mounting sshfs using apple's automounter is here - 

http://virtuallyhyper.com/2013/07/mount-various-file-system-with-autofs-on-mac-os-x-mountain-lion/#mount-sshfs-with-autofs