Sirius satellite radio, 2 radios under 1 account?

I have a sirius satellite radio and I want to get a universal kit for my wife's car, but there is a promotion on for the stratus, I am wondering if I can put a second radio on my account for the price of 1? I am uming that I will have to pay for 2 but just want to be sure, or see if there is any tricks to get a 2 for 1