Instead of

    ssh -R 12345:localhost:22 server.com "sleep 1000; exit"

use

    ssh -R 12345:localhost:22 -n server.com

The -n flag tells ssh to only make a connection, without ever running a shell. This means it even works when you don't have shell access (say, with a command= entry in .authorized_keys).

Also, I cannot recommend envoy enough in lieu of ssh-agent, if you're not using a GUI ssh agent already (e.g OSX keychain or GNOME keyring)

Last, I guarantee you don't want "$@" in those aliases, but either "$*" or $@ (certainly the latter).