Set up an entirely new number on Google Voice. Don't connect it to your mobile number.
Once it's set up, have it forward to your mobile number. It'll give you a 2 digit code, call your mobile number and you'll have to enter that 2 digit number into your mobile phone, to verify that the number you forwarded to is really you.
From then on, when someone calls your Google Voice number, it'll ring on your mobile phone. (You can forward to more than one number at a time, so your mobile phone, your home phone and your wife's phone will all ring when someone calls your GV number.)