I googled IABG and they are an "analysis and test facility for the aviation industry" according to Wikipedia.
I'd guess the item fitted to the main rotor head on that BK117 is possibly a device to load the rotor-head up with a projected lifetime's worth of fatigue and stress in a relatively short time period for test purposes. My other guess would be that it was a device to cancel out vibration but it seems IABG are more concerned with testing the various stresses on components. It doesn't look like the aircraft is fitted with an air data boom so it is possibly a device only for ground-runs.
I could be completely incorrect too!
500 Fan.