Forward local port or socket file to remote socket file

Altough in the time, when the question was asked, it was really impossible, but it is possible nowadays.

You can to both: UNIX=>TCP and UNIX=>UNIX forwarding.

For example:

ssh \
  -R/var/run/mysql.sock:/var/run/mysql.sock \
  -R127.0.0.1:3306:/var/run/mysql.sock \
  somehost

It is possible since OpenSSH 6.7.

Forward a local socket on demand

• Setup SSH public key authentication
• Install socat at both ends
• create a directory locally for your sockets, inaccessible to other users.

export SOCKET_DIR=~/.remote-sockets
mkdir -p $SOCKET_DIR
socat "UNIX-LISTEN:$SOCKET_DIR/mysqld.sock,reuseaddr,fork" \
EXEC:'ssh user@server socat STDIO UNIX-CONNECT\:/var/run/mysqld/mysqld.sock'

then

mysql -S $SOCKET_DIR/mysqld.sock -u mysqluser -p

stolen from forwarding unix domain sockets with ssh and socat