You can (most likely) configure your router to configure a port of your choice for each ant miner and to translate this to 421 the default ssh port for the address of the miner. You will probably need static addresses for the antminer.
But hold on, as far as I know it is not possible to change the default root password on the antminer so that this will give anyone who knows your ip address or scans it and discovers the ports, access to your antminers. I suppose that the worst that they can do is reconfigure the pool for payment, and so long as you detected this it may not be too big a problem, but I would want to be careful about this and would not really be too happy about it.
I do not know much about antminer. But you can connect via a VPN and set your antminer to only allow ssh and other access only to that address. I don't know how to do that or whether antminer supports it but it is definitely worth a research.