Why not have a pulldown switch that goes to the interrupt pin - if the sketch is running and the interrupt occurs low (use the internal pullup on D2), then go into sleep more - and if in sleep mode and the interrupt occurs, wake up.
I was hoping to use the power supply sync to completely cut power to the chip, cutting the total consumed power to nearly zero, as this device will be in storage from time to time for periods of weeks. On looking again at the schematic, yes, it doesn't say the SYNCIN pin can be used as a power switch, however, it also says that pulling it low will 'inactivate' the converter. I didn't see any power consumption specs for the 'inactive' state, so maybe it isn't a stable state meant for periods longer than a high frequency cycle?
My current version of the schematic just has an open circuit on/off switch, but I would really like to use my nice surface mount buttons if possible! any ideas? I would like OFF power consumption to be <.1mA....