Minecraft - Two servers, two subdomains, two ports, don't want to type in :port to connect

I have two minecraft servers, on sub-domains. www.server1.example.com and www.server2.example.com. server1 is port 25565, server2 is port 25566.

When users want to connect to a non-default port in minecraft, they have to specify www.server2.example.com:25566 to connect to the server. On the default port, this is not needed, they can simply connect via www.server1.example.com.

How can I pass along which port they're connecting to on the backside of things, so that users connecting to a non-standard port only have to type in the sub domain?