I don't know if you can convert it. It's sure never been an issue for me. I hunt with an Encore/Pro Hunter 90% of the time, in some very cold temperatures, and honestly, the thought never crossed my mind. The shells are very easy to remove. If I were hunting dangerous game, then an ejector might be a consideration but for the hunting we do here in Canada, the extractor is more than adequate.
If fingers were so numb that you couldn't remove a shell, I doubt you could #### the hammer or pull the trigger either. Pretty much a non-issue I'd say.