Technically, if it's a stripped lower, yes, that's right. But if it has a stock on it, (a folding or collapsible one, preferably) then it retains its preban status.
The big issue is, how's anyone going to know what's clipped to the lower (as in, uppers) if you don't tell anybody?
Let the three little monkeys be your guide.
If my lower shows up in the manufacturer's records as pre-ban, and it's configured into a pre-ban rifle, and there's no evidence that it was sold in stripped condition at any time since that ruling, then I wouldn't worry about it. Not at all. Do you think a jury would even THINK of convicting you when the evidence is a pre-ban serial number on an assembled rifle in a pre-ban configuration?
Proof. It's all about proof. If they can't prove it, they can't convict you on it.
Here's what I'd do as a safety precaution, though: Require the seller to make sure that there is a collapsible stock attached to the pre-ban receiver so that it's definitely in pre-ban configuration during shipping. If you don't have a collapsible stock, buy one from him. If he doesn't have one, get one and send it to him and have him screw it on. It doesn't even have to be tight. That satisfies the letter of the BATF ruling, and that's all that matters.
The 11th Commandment: Don't Get Caught!
CJ