Thanks for the pictures - this is exactly what I had in mind.
You should be able to fit the CSL wheel into the E39 M5 provided the wiring is compatible. This is a potential problem and the main reason why older (pre 2001) E39 cars cannot retrofit the current wheel.
I don't think the new E60 wheel would be compatible with the current E46 CSL (or E39) wheel.
I shall try and specify the alcantara wheel on the E60 and keep you posted on my progress.
Does anyone know if these alcantara wheels start to smell after a while - I wouldn't want that