For this you need:
An iPad/tablet case.
Three packs of Sugru.
A strong neodymium magnet.
A metal washer the same size as the magnet.
A cheap tripod mount with 3/8 inch thread.
And this is how you do:
Open one pack of Sugru and knead it until it's warm. Then use it to glue the washer to the back of the iPad case.
Remove everything but the thread and plate from the 3/8 inch tripod mount. I used one made for GoPro but take what you can find as long as it's cheap.
Open the two remaining packs of Sugru and knead them warm. Then attach the magnet to the tripod mount thread. I made a pattern on the outside of the Sugru to get a better grip, but that's optional.
Wait 24 hours for the Sugru to cure. Then screw the new tripod head on a suitable tripod. I like Joby's bendable GorillaPod models.