I've fixed lower power speakers with the sort of tissue used for model aircraft before, light but strong and conforms well to a curved or textured surface. You could use multiple layers. Several layers fo thin paper will be better than one of thick card as you want some flexibility.
Not a fan of copydex, I'd use PVA diluted 50% with water, as little as you can get away with.
If you can seal the hole, you're good to go for a temporary solution and no bodge on the cone will prevent you from having it properly reconed or replaced in the future.
If it happened when setting up, I would use gaffa tape, one piece on either side of the cone 🙂