The E39 version of BMW (aka 5-series) has an M5 model that apparently
has insufficient trunk room for a "normal" spare tire.  As a
consequence, BMW offers the M-mobility system (basically a pressurized
injected substance) that enables the tire to maintain adequate
inflation until such time the tire can be repaired.  My question is: 
Has BMW come out with a space saver tire for the M5 (E39)? 
Alternatively, are there other spare tire solutions that would work
for the E39 M5?  Of course, all four tires/wheels are different so the
solution would be sub-optimal except it might be better than the M
mobility system.  Thank you.