Drink the beer and think it over? Try the putty approach, if it fails, you can go at it again with your newly emptied beer can.
I\'d think a beer can would be a little too easy to bend after you\'ve painted it though, your banner would be all cracked and ruined.
You can get rolls of tin, aluminum, copper from DIY shops. Home stores, the places you get shingles for your roof and 2x4\'s etc. (not sure where you live so just trying to be clear in case you dont use the same terminology as me) Might be hard to find something thin enough there though. I got a roll of brass shim stock from lee valley, it works great for banners, pennants etc.
www.leevalley.com
click on \"item search\" and do a search for \"brass shim\", if you do buy from here and are considering getting the sampler I\'d advise against it, I have the thickest roll, 0.010\", and can\'t imagine using anything thinner for anything so I\'d just suggest you get that. It is a bit pricey but you can make literally thousands of banners/pennants from that one roll, I doubt I\'ll ever finish the one I\'ve got.