I find it incredibly easy to maintain stacks. AD carries should be in farmville all day, and now you don't even lose all your stacks on death (they changed it to half - you could lose 20 stacks at most), so getting a BT first is even more viable. That said, I generally go for IE first (after Zerk's/Doran's/Vamp Scepter), then PD, then finish BT, LW, and some MR somewhere in between.
What matters most is that you know how to last hit and etc. If you focus on that and not being aggressive constantly, you'll have less deaths and your CS will be higher, meaning your stacks problem will not be an issue both because you'll lose stacks less and you'll gain stacks faster, and most importantly, you will be ahead, so it won't really matter which of those two you get first.
