ISP's using dynamic IP's is pretty much the standard. I haven't heard of anyone else having a problem like this and I sure don't and I use Comcast.
Your router should be able to route the traffic regardless of the ISP changing IP's. Your mining software only see's the gateway IP, AKA your router address.
Are you still using OS/2? Does it still exist? I used it about 15 years ago, really loved it, but it seemed to ..... disappear ... from my gaze at least.