Drill out holes through entire bumper rail

Fig 1: Identifying Hole Center Marks And Hole Saw Drill Bit Diameter

Courtesy of VOLVO CARS OF NORTH AMERICA.

Turn the bumper rail so that the studs point downwards. Place the bumper rail on a suitable underlay
Remove the foam layer
Pre drill 3 mm (1/8") diameter holes at the existing marks
Using the 70 mm (2 3/4") diameter hole saw, drill out the holes through the entire bumper rail
When the hole saw reaches the bottom, turn the bumper rail. Drill from the other side.
NOTE:
Use a long central drill bit with the hole saw.