HRoth - 1:40 am on Aug 31, 2010 (gmt 0)
stamps.com will allow you to force an address. It will say it can't be added to the address book, big deal. That is one big advantage over usps.com. I've had that same experience, where usps.com won't take an address. I'll check it on Google and it's real.
The other service is Endicia. I looked at that too but now I can't remember why I didn't choose it.