Set up in whatever position you can easily do a ollie half kickflip from, although it's a good idea to start with your front foot fairly close to the nose, so the catch is easier.

Pop like a regular kickflip, but flick light enough that you can keep your front foot close. The board only has to flip to around half, so there's no need to kick your leg out at all, it can be done using your ankle alone.

As the board finishes the half flip, bring your back foot forward to meet the tail of the board. The idea is to push the board around in a shove it half flip, just like you would out of a regular casper.

Some people do this trick using only their front foot, making the board to sort of a backside half front foot impossible. That way is much easier, since you only have to hook the board and throw it around, but I prefer to do them like a real casper in the air. In the end, it's up to personal choice.

Just like in a regular casper shove it, your front foot will end up on the board first. All there is left to do is stay over the board and commit to landing it.