Here is how to do a 50-50 Casper. This trick is also known as Truckstand and No Handed 50-50.
A flatland skating stance more accurately called a no handed 50-50. In a truckstand the skateboard is held almost upright with the top of the deck facing the ground slightly and balancing on one of it's kicktails. The skateboarders 'back' or bottom foot stands on the bottom truck while his 'front' or top foot is hooked on the other side of the deck to keep the skateboard upright, usually but not always near the top (it is positioned lower down when the skater wants to do a Pogo.