Replying to Keeping hands warm while filming

What do you guys do to keep your hands warm while filming? I can get by with pretty thick mitts while filming on a tripod or for fisheye stuff where I dont need to pull focus, but for handheld stuff or when filming with shoulder cameras I have yet to find a good solution as you really need thin gloves to be able to focus and find all the buttons. Any experience with hand warmers that works or maybe its worth trying to cut open a pair of mitts to still cover the top of your hand while having thinner gloves inside?