ssh proxycommand equivalent on server

Question

Lets say we have three machines me, proxy, server

I would like to have an ssh connection to server, so normally I would do

me$ ssh proxy
proxy$ ssh server
server$ # and here we are

ssh proxy solution that is entirely client side would be:

$ cat .ssh/config

Host proxy
    HostName proxy.ip

Host server
    HostName server.ip
    ProxyCommand ssh proxy -W %h:%p

But If I wolud want to force this proxycommand on my server, I would edit my authorized_keys file like this:

$ cat .ssh/authorized_keys

command="ssh user@proxy" ssh-rsa AAA...444 omg@themiddleofnowhere

Okay: these two solutions work the for ssh, but for commands such as rsync and scp and others, the first solution works, while the second one fails.

Question: how can I force the ssh proxy command on my server and still allow commands like rsync and scp to work normally?