Basically, it's a spray made by 3M that will waterproof pretty much any type of fabric out there.
Here's a few websites about it:
I'd recommend testing it out on a "crap" pair first just to make sure it doesn't make things bleed/run, but if it works you'd have a great way of waterproofing them!
Oh my heavens! Thank you so much, I swear I have been looking forever.