The commercial pilot was practicing a forced landing with a certified flight instructor (CFI) providing instruction. After the maneuver was initiated, the CFI recognized the helicopter was not settling quickly enough so he limited the amount of collective the commercial pilot could apply. As the helicopter slowed, the main rotor revolutions per minute (rpm) slowed. After the rear of the skids touched down the main rotor rpm continued to decay, and the front of the skids dropped eight to 10 inches onto the runway. During the landing two main rotor blades contacted both auxiliary fins on the tail boom. Examination of the damaged main rotor blades revealed substantial damage due to delamination and inner core damage on both blades.