I've done a similar setup, but for a minimalist mount, used two 12in rulers, and gaff tape to make a hinge, a strap connecting the other ends, and a stop on one of them. So a heavy thinkpad sits on the desk ruler, leaning back against the other and the strap, with the bottom keyboard edge sitting between strap and stop. It's fragile, and I fear someday there will be a bump, crash, and sadness, but it's light, compact, and easily recreated.
I've done a similar setup, but for a minimalist mount, used two 12in rulers, and gaff tape to make a hinge, a strap connecting the other ends, and a stop on one of them. So a heavy thinkpad sits on the desk ruler, leaning back against the other and the strap, with the bottom keyboard edge sitting between strap and stop. It's fragile, and I fear someday there will be a bump, crash, and sadness, but it's light, compact, and easily recreated.