Rumour is that there will be a paddle shift conversion available from an aftermarket supplier (after all BMW's have offered SMG on several models e.g. M3 CSL) but not sure when this will be available or who it is (so not much help then!)...
Merz & Pabst are developing a paddle conversion, there may be others developing one as well, with a known German BMW tuning company. This is for the ZF-automatic box in the S4 (et al), the SMG (sequential manual box) box in the M3 is an electronically controlled manual, a normal 6-speed manual with electronics organising the changing - despite the sequential moniker, if I remember correctly - perhaps Simon or someone else can confirm. Not quite the same thing as the ZF-automatic Morgan use, which has more similarities to the box in the Maserati and the Jaguar XJ (both with paddles).