As a somewhat painful alternative that's perfectly legal, you can just ESN swap the phones depending on which one you want to use at a given time. Best practice is to actually turn off the phone (or at least the data connection if you use Exchange OTA) for a few minutes, do the ESN swap, then turn the activated phone on. Do that twice a day for a year and you'll be really sick of it, but at least it'll work and no one will hassle you.
