Let me think...... needless fuel burn while in flight with passengers on borad......... I like the pen idea better.
I like both ideas. It's not the fuel burn that really matters on the APU, by the way. What matters is the operating time. Pinnacle pays for the APU by a formula that uses a ratio of APU hours to block hours. The more time that the APU is operated, the more they pay, and the penalties can be very hefty.