Yes, it can be done. For this, the remote server has to support local port forwarding (which might be disabled for security reasons). What you bascially do, you instruct the remote server to open a tunnel to a server in the other network for you:
ssh -fL 127.0.0.1:someport:host.in.the.remote.net:22 proxy.host
someport should be an unused port on your machine (for example 2222), host.in.the.remote.net should be the hostname or IP of the development machine you eventually want to connect to, from within the network of the proxy.host, which is the intermediate server you have to go through. -f
instructs ssh to detach from the terminal after the connection is established.
You run this command, and after it is in the background, the remote machine's ssh port can be referred to as 127.0.0.1:someport
and can be used as such by sshfs. I don't know of a way to automate this though, but you should easily be able to script it.
Make sure you clear this action with the remote administrator beforehands if you're unsure about the policies. You may need to change the 22
in the first command if the development machine serves ssh on a different port.