Electricblue

I am now the proud owner of a Jaguar S-Type R, it arrives next Tuesday. One of the first things I need to do is change the tyres, I would like to use Michelin Cross-Climates, I use them on all my cars and just love them. Clearly demonstrating I didn't do my research, I have discovered that the front tyres are 245/40/18 (8" wheels) whilst the rears are 275/35/18 (9.5" wheels). Rears tyres are not available. Has anyone got any suggestions? Change the rear wheels for the 8" for example?