I grabbed a simple set of 6 inch tall rhino ramps and tow pieces of 4×4. I laid the wood side-by-side in the front of the bed. Place the rhino ramps up against the wood. This acts just like an ATV riser but without the bigger height. The 6 inch height difference lose the rear axle in about three or 4 inches.
The forward movement is enough to bring the rear axle center just inside the edge of the bed about an inch and a half. This means the majority of the rear weight is on the bed itself and not the tailgate. The tires still contact the tailgate but without a great deal of weight and it will not flop around.
This picture shows from the inside of the wheel inch clearance into the bed.
Another photo showing that the entire weight of the ATV is inside the bed.
The ramps have a 12,000 pound rating.
Rear photo showing the tires and wheels inside the bed.