You need heat to flatten the sheets because they're covered with a plastic film, that's why they will always get back to their round shape unless you heat them or grind them thoroughly (the inner side which is in contact with the drink).

The good thing with the heating method is your sheets will tend to come back to their flat form if bent moderately (i.e. as long as the plastic film is stronger than the aluminum lack of elasticity), while they will remain bent with grinding (no counterforce).

If you want to give your sheets a specific shape, e.g. to sheet a wing or a hull, pin them (liquid side outwards) and use a (cooking) blowtorch to set them to shape. When unpinning, they will keep their form.

Epoxy (or most plastic glues) will work on the liquid side if you sand it lightly first (100 grit or lower), don't go to the metal. Nothing will work on the outside (the layer of plastic is too thin).