It can be done, but it's not a bolt-on! :-)
Bottom line: if you want a 4-wheel Brembo kit for your M5 and you want to keep your 17" winter (or track) wheels, it is possible, but you will have to get slightly creative with some air tools. Photos of the "creative" part are down below.
Here are some shots of my car, taken this afternoon. The 4-wheel Mov'it kit is now for sale, but I think it's already spoken for. I'll let you know if my buyer changes his mind. I was asking $3400 for it and paid $6K from Ultimate Garage.
Front 355mm x 32mm rotors with Brembo 4-piston F50 caliper
Rear 345mm x 28mm rotors with Brembo 4-piston caliper (28/30mm pistons)
It looks pretty tight now, but it was even tighter when I tried to bolt it on. Despite reassurances from Brembo that the Style 66M wheel would clear, it did not. In fact, with a 5mm spacer, the caliper was still touching the barrel of the wheel where it (the wheel) starts to neck down in size.
I was not going to let this brake kit defeat me, so out came the air tools!
After putting a 45 degree angle at the outside edges and then filing down the high spot of one wheel weight, there was a minimum of 1.5mm clearance at the closest point. That's about where you want to draw the line. I used some 1500 degree engine paint on the bare aluminum where I ground the calipers. The paint is silver, but you can't see it with the wheels installed, so I won't bother to paint it red.
I bedded the brakes in this afternoon and they feel pretty good. Pedal travel is slightly longer than the Mov'it 322mmm brakes, but that's to be expected with the F50's bigger caliper pistons. Also, the pads still need another round of bedding. I expect it will firm up some more.
The rear brakes require a special spacer, since the longer rear hub lip prevents the use of a standard E39 hubcentric spacer. I had to stack a 3mm universal spacer underneath a 10mm hubcentric in order to get it to work. I have a shop building me 12mm hubcentric spacers which will then become available as the first rear hubcentric spacer for an E39.
An interesting side benefit is that the parking brakes work far better than they have ever worked before!
Talk about squeezing it in there?! 
J/K
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