I've solved the problem! Get a Rolleiflex SL66 instead of the Hassy! (actually I have both). After all "The Flash Synchronization speed up to 1/30 second guarantees sharp and well illuminated pictures..."
From the Rolleiflex SL66 product description on eBay (where this originally came from I do not know):
The Rolleiflex SL66 is a film camera with 6x6cm image format. The shutter speed range of this Rollei film camera is 1 - 1/1000 second that enabling better effects on the appearance of moving objects. The Flash Synchronization speed up to 1/30 second guarantees sharp and well illuminated pictures on this Rollei camera. The 80 - 150mm focal length of this Rollei film camera covers wide angle shot with precision, giving you even the minutest detail of the subject. You can also tilt the lens of this Rollei camera up and down upto 8 degrees. The TTL metering with special hood SL66 in the Rolleiflex SL66 camera lets you choose the optimal exposure for fast or slow speed snapshots.