Could you rig a 4x4 welding hood lens somehow ?
Probably since I know there are square filter holders out there... but I'm thinking of getting some mylar or other plastic film that they use for things like this. This will likely be a one off picture so instead of investing in a camera filter made for the job ( about $60 or so which isn't bad considering what it is ), I can use a little lower quality film and make a way to attach it to the lens a number of different ways that I can think of.
The main issue with me will be affording the fuel probably... and finding a spot that someone will allow me to shoot the pics from. ( that last is a hint, it's just too soon to really ask since I'm uncertain if I can go yet ).