I am (was) confronting a similar dilemma. Based in Sacramento (SMF), just now I booked SMF - BOS out on Decemebr 24, returning December 25. That trip still leaves me a few miles short so, during the last week of December, I'll make a quick business trip up or down the West Coast.

When researching potential solutions, I found fares to BOS as a destination to be much more reasonable than other East Coast destinations. At $0.085 per mile, this mileage run was far from free. That said, this will be my first and only mileage run of 2010, so the $0.085 per mile price seemed justified.

Another thought: I found air fares to Frankfurt, Germany (FRA) to be pretty reasonable, about $0.06 per mile.