the trick (as I learned it from watching OCC ) is that you need to stretch the middle of the material, not just bend it. That's what those wheels do. That would clearly mess up your diamond pattern. I'm pretty sure you can't heat up aluminum enough for it to mould it under hand pressure. Something like the beanbag suggestions is where I'd be going - starting with just trying to make a dish shape in a piece of scrap.

This is all drawing on my vast legacy of tv watching skills.