If you don't have an iPad box, try bendable cardboard or plastic cards. Plastic will make it more durable but basically anything that's kinda hard and can be wrapped around the corner will do.
The following steps are not really necessary but I want it to look nice and stay on the phone corner really nicely :-P
Here are some photos taken with the DIY macro lens
Special thanks to my mom who has done the crafty parts! :D