Wheel Fitment on a 2012 CLS 550 4 matic (Would like to run a square setup)

I would like to go to a square setup on my car

The front rims are 18x8.5 with a  34.5mm offset with 255/40ZR18 tires

The rear are 18x9.5 with a 48mm offset with 285/35ZR18 tires.

I have 4 of each as I have snows and summer tires mounted for easy tire swaps.

The problem is that the snow tires (blizacks) are only available in the size for the front and per tire rack you want t run that size on all four.  The problem is that they look stretched on the rear rims.  It is just ugly.  Really ugly. 

What I would like to do is put the four snows 255/40ZR18 on the front rims that are 8.5" wide and four summer tires 285/35ZR18 on the 9.5" rear rims and run them that way.  So I would have a square setup.    The issue I am sure is going to be the back spacing interfering with things.  I could just try it but would rather not experiment on my car and cut a tire or something.

Anyone know if I can do this?

The front wheels should fit on the rear axle but the rear wheels won't fit up front without a spacer and even then the tires might rub on the guards as 255s seem to be the widest tire people are running up front on W218s. If you want to test, take a rear, put it on the front, rub chalk on the tires (top of the tread, inner sidewall up top and on the sides, outer sidewall around the curvature of the guards) and move the steering through its range of movement. If there's any chalk transfer, that's where it will rub.

I think you'll want to go on car-part.com and buy two "A" condition front wheels, and install those on the rear.

I had a previous generation CLS63 and the rear wheels (19x10 or 19x9.5 with 285s) would fit on the front.  It was close, but they did.  I ran it that way for thousands of miles, including One Lap.  

Take one of the rear wheels and put it up front and give it a try.  

Probably the easy button is to find another pair of front wheels for the snow tires. With how the offsets are all the extra width is on the inside so it should look fine. Alternatively, if you branch out into other brands, there should be options for 285s, or at least 275s. With snow tires it's not uncommon to go a size narrower than stock, I'd even think about doing 245/275s.