The plastic he uses is just super cheap painter's tarp, the cheapest, super thin crap you buy at home depot. That works best for this. Of course he has mastered this method and it's not easy. this is essentially what I did with peel ply the other day on the top board of GF2. I would have used plastic if I had some handy, but by the time I realized I wanted to wrap the edges all I had handy was peel ply.
Plastic won't reduce the excess resin like peel ply will, and it doesn't give that great "tooth" that makes the next layer adhere so well, but for work like this it's best.
You can tell Jimmy is just super-freaking-human at this because his tinted glass is as consistent as paint. That ain't normal. He cracked me up talking about not wasting epoxy--I've never mixed a batch of epoxy that large in my life. I bet half of that went in the trashcan. Jimmy's shoes are as heinous as they sound--2/3 epoxy and he wears them barefoot. I wouldn't put those on my feet for a free custom board.