As with everything, you have to decide if the effort is worth the pay-off. Teaching a dog to "sometimes" use pads and sometimes not will require a ton of effort and result in a number of unwanted mistakes (most likely.) I would probably try to desensitize a dog to the rain and hire a dog-walker when it was icey, or look at cleats that make the footing more stable for me.
I might also look at the indoor-potty areas that look more like the out-doors with turf and the raised platform. That would be an easier training step. Then you could just lay a piece of turf outside in your dogs favorite training area and teach your dog to pee on it until your dog liked turf and would use the indoor area when they got desperate. I would have the "loo" out all of the time and expect it to be used sometimes, even when I was able to walk my dog.
To pad train, I would lay a bunch of pads outside in my dogs favorite spot, keep my dog on leash, and praise lavishly for peeing on or near them. This would be miserable training that would have to be maintained to keep it clear. For me, it wouldn't be worth it. I would go with the turf area if I couldn't find a way to deal with the footing in the ice.