Network-dependent ~/.ssh/config?

In the office, I can connect to internal machines without a proxy, but need a proxy for external connections. Outside of the office, I can connect to other external machines without a proxy, but need to use one of 2 proxies to connect to internal machines.

If I can figure out a way to autodetect what network I'm on, can I instruct ssh to load the appropriate config file?

If not, is there a more elegant solution than writing a shell script to symlink the appropriate config file to ~/.ssh/config (my best idea so far)?

Edit: I think @pcm and JonnyRo understood my question and I'll try what they suggest, but just to be clear, I want

|--------\    Dest   | abc.example.com | xyz.external.org |
| Source  \---------\|                 |                  |
|--------------------+-----------------+------------------|
| example.com office | No Proxy        | Proxy            |
| outside            | Proxy           | No Proxy         |

Depending on how your proxy is configured, you can simply build an SSH config entry that works in either situation. For example on one network I regularly use I have to ssh to an intermediate host before I can make an outbound connection. So basically I setup a configuration that looks like this.

# proxy ssh 
Host *%sshproxy
    ProxyCommand ssh [email protected] /bin/netcat -w 1 $(echo %h | cut -d%% -f1) 22

Host myhost.example.org
    HostName 172.16.24.1

Host otherhost.example.com
    HostName 192.168.57.12

So when I don't need to use a proxy, I can simply run a command like ssh myhost.example.org and get connected, but when I do need the proxy, I run the command ssh myhost.example.org%sshproxy.

I suspect you could probably setup some kind of alias or auto-complete setting that would automatically append the %proxy bit.