I've seen people make skis that just strap on to the tires, so all you would need is a piece of steel wide enough to cover the tire and allow for a skirt of some sort along the side. Then of course the length to ensure it stays afloat and have it curve up so the snow gets pushed under it.
I had planned on doing this last winter for my DB30 but it wouldn't have floated even if you strapped a ton of helium balloons "UP!" style. Have a long piece of 1/8" thick steel, curve it up, add skirts, then weld on eye bolts for a strap to hold it on. Use a 1/2"x1/2" sq solid bar for the runner so it has room to wear. Then high gloss paint and wax it down so it sheds water so fast it could deflect rain back into the sky.
My thoughts anyways.