That's true and for a long time the ATF was very unreasonable about that issue.
Now, it seems, they have backed off and only consider "constructive possesion" if the restricted device is the only possible build.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.