Two I2C slave devices, only one standard address.

I am using the SI570 I2C synthesizer. The SI570 is only available with one I2C address (55), unless one is willing to pay the company for a unique address. Is there a way to load two synthesizers with the Uno over the wire.h ports? Can I use a couple digital pins for this purpose?

Silabs Si570 : http://www.silabs.com/products/clocksoscillators/oscillators/Pages/i2c-oscillator.aspx

The best option is to use a I2C multiplexer, like this one : http://www.adafruit.com/product/2717