Surface Pro 3 Hand Strap

Required to make this is a one inch belt and a "strap adjuster" like this:

https://www.thingiverse.com/thing:2613356

I suggest finding a nylon strap, hopefully repurposing a strap off a damaged backpack or bag. They can also be bought individuall or in bulk. I used cotton, which was a tight fit.

You can either go with supports, and if you're lucky you can use "touching buildplate only" but have it still support the bridge some, or you can go with no supports and just rely on bridging. Using a thinner strap than I did will make threading it easier.

Doesn't really leave much room for the camera, so you could really just print two bottoms (or two tops).
The top one does work well one the bottom screen when its set up in portrait mode, as it leaves good room for the windows button