We've always had to put a CC down and they'll take out the first nights room rate (within a week), you pay the rest on arrival. However, we were allowed to send in payments in 06. We called and asked about making payments to the balance before we arrived and was told you can send in payments with a certain form (that SOG had to send us, they sent several), we got the payment forms and then decided just to wait and pay when we arrived.
It'd be better if you could do it on the phone (and maybe you can by now? I don't know), but if you are insistent you can go about paying before you arrive in other ways (like I mentioned). Do take into consideration this was in 06 so the policy may have changed since then.