GSM and CDMA are entirely different types of wireless.
Therefor, there is a different type of antenna for either one. If your phone has a GSM antenna, it will not be able to see CDMA signals. It's hardware, not software, so there is no way to "hack" your phone and make the change that way. You'll need to either buy a new phone, or use your current network.
It's kind of like trying to use a Bluetooth receiver to pick up WiFi signals.. it just can't be done.