I recently ran across this listing for a a homemade tire, but looking at the closeup photos it’s clear that each rim has it’s own tire.
On a unicycle this would probably be pretty hard to steer, but on snow/sand it might work. A 26" Conundrum frame might be able to accommodate two 29" KH XC rims (@ 38mm each), but I would think a custom frame would be needed to go really wide.
I wanted to do that with a few crappy rims I had at home, but I need to find steel rims so my friend can weld them together. But I wanted to use one single time for both. On the link you posted it looks like he used 2 trials rims (47mm each) so it makes it really really wide (94mm wide 
) , I would’ve use some skinnier rim, but not too skinny.
This definitely looks like a project for Saskatchewanian.
probably just as wide or wider 1st link is your rim second link is your tire
I’ve thought about making a wheel like this, but using a single tire. I was thinking of using a couple of 700c Weinmann Concave rims to make a 29er wheel. Once they are together it would be a nice width, and it should be very strong if not a bit on the heavy side.
lol, +1