For deep-firewalled machines that you need to be able to ssh access (dhcp-depth or otherwise)

From the machine you can't access (localhost), connect to one that is accessible (remotehost):
ssh -fNR #:localhost:22 -D # remotehost

From the machine you can access (remotehost), connect through the tunnel to the one that you couldn't access before:
ssh -p # localhost


Example:
dayid@clugg> ssh -fNR 9090:localhost:22 -D 9090 falkor

dayid@jones> ssh falkor
dayid@falkor> ssh -p 9090 localhost
dayid@clugg>