I would like to use ZPool as a backup pool only when the main pool is offline. I guess the easiest way to implement would be to divide all the profits by 10, so the main pool would always appear more profitable.

Any drawback to that solution by just adding a zero to the end of the divisor? Only one I can think of right now is forgetting about it when updating the scripts -- so a custom multiplier per pool in the config would be nice...