Since you can never find any of the Regis in DW, how would you make it have its hidden ability?
You can't. The only way to make a pokemon have its hidden ability is to obtain it through the Dream World.
In your case, the Regis will probably be available through an event.
How to change your username How to add a user avatar Why was my post hidden? The points system Question etiquette Flags vs Downvotes Anime FAQ
Type a Pokemon name, type, move or ability to see instant results.