One for those of you into etching.
How about an etched washer that fits either over the axle or over the boss on the rear of the drivers with a slot in it to solder the crankpin to.
This would fit behind the wheel, and obvoiusly would not be of a diameter that could be see between the spokes, may be more sophisticated in shape to do this.
It would provide a solid location which is prevented from turning by the fact that it is fitted round the axle/wheel boss.
It would also need to be fairly thin as it is usually the driver where you want most side to side allowance for curves.
Over to you guys
Phil