I have fitted perspex visors to my 2006 S1 Roadster, & I certainly don't posses the 'fettling skills' of Dave W etc! But was able to modify them to fit around the rear view mirror, just needed the fixings to suit the windscreen studs.
There is a previous thread on here somewhere, they are advertised as Mini visors, available from c-t-sspares on e-bay in a number of colours
