I am not sure you can even order the TIW by mail if all you have is a voucher. I think you have to have an actual AP and they will ask for you AP number, so they'd be able to tell if you had an AP or a voucher.
If you have an AP now, you can call and get one now to be mailed. But unless you need it before you go to a park, then you should probably buy it when you have gotten your AP. You would have to go to a park or DTD to get the AP anyway, as you can't get one at a resort.