That's what I mean - M Mode. Yes, you can use AE-L, but with panoramas I find that I'm already focused on so many other things that I'm concentrating on (20% overlap, level horizon and movement, etc.) that keeping my finger on AE-L is just one more thing. And I also find that the exposure at the first frame of most panoramas isn't always best, so you have to lock the exposure where you want it metered, and then reframe for the first exposure and shoot. This is even more complicated by the fact that I like to shoot panoramas vertically.
My solution, set aperture the way you want it, meter and focus lock on the subject. Turn off autofocus, change to M mode and dial in the settings I got when I metered in A. Now I can concentrate on my framing.