Using the ChromeOS host shell aka crosh for SOCKS5 tunneling
Set up SSH access to the host sshd, either manually starting it or by removing the read-only protection on the rootfs. See this gist on how to do it manually which is the safest and least intrusive option. https://gist.github.com/espoelstra/c910a8f5de6ba16d09fdb2014a5d843c
Once you've gotten ssh access to the chronos user's shell you can setup an SSH config that allows forwarding of your SSH key to the next host, in this case the jump server or bastion host.