The account stacking issues aren't limited to people on opposite coasts. The original offenders were those who subscribed to residential service and took their setups to work. Some spotbeams cover upwards of 8,000 square miles. While this answers the question of opposite coasters, it is only a partial solution.It ought to be possible for dish to download some software that tells the receivers to check for signal on a particular spot beam that they shouldn't get in their DMA and if a signal is present, to kick it off.
The real solution probably involves GPS and some sort of LNB serial number addressing scheme, but that would take months to implement and years to install.