Sensors will go to sleep once the ignition is turned off. Waking them up just requires some activity. Ride the bike in excess of 30km/h and they automatically wake up. Deflating the tyre quickly is another way to get them active.
However, having said that, I have rarely been able to configure NEW sensors by this means. Creating some activity wakes them up but leave them in Neverland, and without knowing the sensor ID, it remains very difficult to get them configured. I have also found that where more that one sensor is present, Sensor Learning will be unsuccessful.
The tool I use is a Ateq VT30.
It does not only the BMW sensors but almost any known sensor out there. Also has periodic software updates to add newer sensors for a huge range of vehicles.
Simply hold the unit near the sensor, push the transmit key and the display reads the ID, tyre pressure etc, etc. This ID can then be entered manually on the bike.