Fortunately I live close enough to home such that I can drive to campus in a reasonable amount of time and so I've never done this, but it sounds like an intriguing idea -
What if you just outright buy a 15+ year old used, reliable, Japanese econobox (Civic? Accord?) outright? It'll probably cost you $3k or $4k. You drive it for the few months you're at college, and then you sell it once you're ready. Your total cost of ownership will be depreciation plus liability insurance (cheaper than full coverage) plus opportunity costs of not having that money invested.
A '99 Civic EX goes for $3900. A '98 Civic EX goes for around $3700. A '97 Civic EX goes for around $3400. Granted I've presented just 3 data points, but at this stage (15+ year old car), the depreciation curve seems to be relatively shallow.
Here's a fringe benefit - you'll eventually get used to driving a slow and relatively boring economy car while at college. This will make coming back to your 335iS all the more pleasurable.
Second fringe benefit - you get to indulge in a little "stealth wealth" this way
. Driving a car (or hell, just
living) well below your means can be an interesting and insightful experience.
Anyways, it's just something to think about. I don't know how this plan would compare to zipcar rentals.