The so called "bumper" is far to weak to hold anything, Don't even stand on it.
Some people have reported adding custom welding to the frame underneath and carrying bikes successfully. As ko777 says, a rear bike rack also runs the risk of voiding your warranty. If you decide to pursue this, make sure of you can maintain the gross vehicle weight within the rating and while keeping at least 10% of the weight on the tongue.
2012 Rockwood A122S
2008 Toyota Tundra Double Cab 4X4
Former owner of a 2002 Coleman Niagara GTE