the following is advice i was given a number of times when contemplating if i wanted to try and build the rifle my wife wants, in a Pre-ban config after the sunset...
IF i repeat IF someone is somehow worried that following the advice given by WildAlaska above might get them in trouble there IS another loophole that the ATF has left us poor put upon gunowners...
get REAL sneaky, BATF says if the Pre-ban parts are not not owned by YOU or within your direct control, IE you do NOT have easy acess to them (as in locked in a cabinet you do not have key to) then you can have a post ban weapon/lower in the same home.
ya married?? got a roommate you trust?? give the other person teh money, have them buy a pre-ban complete upper, lock it away in a safe or even filing cabinet that YOU do NOT have a keep or combo to. go buy a lower in whatever config makes you happy, stripped, complete whatever, but have it COMPLETE by Sept 14th... IF/when the ban sunsets, give your buddy/spouse/whatever a dollar for keeping it for you and have them write out a receipt giving it to you, assemble the rifle.
you now have a complete legal rifle.