As far as I'm concerned you can do that provided that:
1) you have public IP and sshd server running OR
2) if you are in intranet and you can set up port forwarding on your router so as port 22 will be redirected to your machine
if 1) or 2) are the case for you and macos machine has sshd server running. Do the following on macos whenever you want to have access to it (make script from it and give it to macos owners):
macos$ ssh -R 65022:localhost:22 root@<yourmachine_ip_address>
What it does is forwarding macos's sshd server on your port 65022.
Now you can simply ssh to port 65022:
yourlocalmachine$ ssh -p 65022 firstname.lastname@example.org
and you should be on macos now.
By the way: yourmachine_ip_address can be a third machine with sshd access, which you own and with public IP address. Than in last step you would connect with it this way:
yourlocalmachine$ ssh -p 65022 root@<yourmachine_ip_address>
WARNING: I'm not 100% sure it will work (I haven't tested it yet), but it's interesting - I will try it as soon as I get back home :)
UPDATE: I've tested it - it works like a charm.
UPDATE 2: In second case (when we use third machine),
GatewayPorts yes has to be set in /etc/sshd/sshd_config file on this machine.