I haven't used (or even seen in real life) the Surface, but I would expect using the stand would be a challenge. It just feels to risky to put that tine edge close to your knees; the screen would drop on the floor too easily. That means you will have to move the edge of the screen at least, say, 15 cm from your knees. Also, having that 'one, steep, angle' for the stand would mean that looking at the screen would be a problem.
So, I would guess using the stand is out. That leaves placing the screen flat on your upper legs with the keyboard in front of it. In that setup, I am still worried about the keyboard detaching from the screen, and the screen dropping on the floor. The keyboard would have to be attached fairly firmly to the screen for that setup to feel secure. It also would place the screen in an awkward location for reading: too far away, and at an inconvenient angle. So, for that setup, I expect you will want something that wraps both the underside of the keyboard and the back of the screen, and props up the screen by, say, 10 cm. I guess something like that will pop up on Kickstarter soon.
So, I would guess using the stand is out. That leaves placing the screen flat on your upper legs with the keyboard in front of it. In that setup, I am still worried about the keyboard detaching from the screen, and the screen dropping on the floor. The keyboard would have to be attached fairly firmly to the screen for that setup to feel secure. It also would place the screen in an awkward location for reading: too far away, and at an inconvenient angle. So, for that setup, I expect you will want something that wraps both the underside of the keyboard and the back of the screen, and props up the screen by, say, 10 cm. I guess something like that will pop up on Kickstarter soon.