Hi JJW, I replaced mine (slash six) a couple of years ago using bolts, as per Snowbum's article. See here, for a great deal of information -
http://bmwmotorcycletech.info/rearwhlsplines.htm
The /6 uses 1/4" rivets, so 1/4" bolts are recommended. I note that the /5 uses 5mm rivets/bolts but the method is the same.
For mine, I used 1/4" Allen head bolts. The washers under the bolt heads need to be shaped to fit between the webbing on the /6 hub -
To do this shaping I did this, and ground the flats using an inverted belt sander -
On the inside, the nyloc nuts also needed shaping on the belt sander. I ran a bolt through from the normal side of the nuts first to cut a thread through the nylon bit, then withdrew and screwed through from the 'wrong' side so I had something to hang on to while sanding.
It all went quite easily, once I understood Snowbum's article (always the hard part). I also had the mating part in the final drive built up with weld and re-machined, but there are other ways to skin that particular cat.