Switch the power to it, using an I/O pin, and either a transistor or FET switch. Even if it has a shut-off capability, they still waste a certain amount of power.
I would also suggest you increase the sleep time (at least temporarily), as repeatedly coming out of sleep while measuring makes it more difficult to measure - to measure mine I temporarily switch the TMR off, so it never comes out of sleep. Then I measure again, without sleep at all, then measure how long it spends out of sleep during normal functioning (using a scope) - a bit of simple maths then gives you the average current consumption.
In my case I was amazed how little time it spends out of sleep, only a few micro-seconds out of every second.