Another option for you e70 owners.
There are new hub adapter spacers that convert the 74mm hub (e70) to 72.5mm hub (the rear on the e71)...
this avoids the boring out of the rear wheels. Link below:

Home Page > Search > es1899557 es1905746 > ES#1899557 Wheel Adapter - 15mm (DRA) - 3075740725

They are 15mm H&R spacers (best out there) and require extended lug nuts. ECS tuning sells them.

what is needed:

15mm Wheel Adapter Spacers (comes as a pair)
Part number 1899557
$124.76

Extended Lug Nuts
Part number 252737 (comes as a set of 5) 2 sets are needed
$12.95 per set

Total Cost: $150.66 (not sure if shipping will be added)

These will push out the rears a total of 17mm which is just over a half an inch (.67 of an inch to be exact). They will fit flush with no rubbing - extended flares are recommended to complete look if you don't have the Sport Package yet not necessary.

Another Xoutpost member (e70 owner) bored out these wheels and added the larger 20mm spacers just to widen the look