In theory, it's possible. Now, whether it would be honored by BMW as a warranty issue, is an other thing altogether! It would need to be engineered well to maintain the battery integrity and discharge limits. Failing that, it would likely damage the battery, and being an unintended use of the battery, probably void the battery warranty.
To be useful, it would take a pretty hefty (and expensive, especially if you wanted a sinewave) inverter of any decent size.
Note, BMW has recently promoted a use for 'old' LiOn battery packs for power buffers for the grid, and will be promoting them as a way to recycle the battery packs as they reach their service limit on a vehicle...they'll still have a lot of capacity for use as backup for things like solar or wind-powered generation, and make sense verses dismantling them and recycling their guts right away. They'd probably have a large number of years of life left when used in that capacity.