...And we have a winner. It was only +5F this morning, car started up fine, no funny noises or excess smoke (just typical brrr mist from the exhaust like every other car on the road). After 10+ minutes highway driving the oil sensor finally gave me a reading, 2 ticks above the bottom. As I kept driving, it went up to 3 green ticks. Went out for another half-hour at lunch, and at the end I had 5 green boxes above the tapered region above the oil pan. Now I'm wondering, if I went further/longer/warmer, if it would report an overfill...
After parking at lunch, I opened the fill cap and let it vent for 5 minutes - a light float of mist that made me happy to see moisture leaving the system.
As for the steady increase in level that others have seen, I'm assuming that colder oil sticks more to internal passages and walls, where as the car heats up more oil falls to the sump to be measured.
End result = happy car, no service call or tow truck, no $200 replacement sensor. Thanks to Bimmerfest.com and Nube1kenobi for posting the SIB!